ACORN INVESTMENT TRUST
485BPOS, 1998-10-15
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<PAGE>
    
   As filed with the Securities and Exchange Commission on October 15, 1998.  
    
                                         Securities Act registration no. 2-34223
                                        Investment Company Act file no. 811-1829
- --------------------------------------------------------------------------------

                      SECURITIES AND EXCHANGE COMMISSION
                            Washington, D.C.  20549

                                   FORM N-1A

                             --------------------

            REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933

                        Post-Effective Amendment No. 63   

                                      and

        REGISTRATION STATEMENT UNDER THE INVESTMENT COMPANY ACT OF 1940

                               Amendment No. 38
    
                             --------------------

                            ACORN INVESTMENT TRUST
                                 (Registrant)

                      227 West Monroe Street, Suite 3000
                           Chicago, Illinois  60606

                        Telephone number: 312/634-9200

                             --------------------

   Ralph Wanger                            Janet D. Olsen
   Acorn Investment Trust                  Bell, Boyd & Lloyd
   227 West Monroe Street, Suite 3000      70 West Madison Street, Suite 3300
   Chicago, Illinois  60606                Chicago, Illinois  60602
                              (Agents for service)

                             --------------------

                Amending Parts A, B, and C, and filing exhibits

                             --------------------

It is proposed that this filing will become effective:

             [ ]  immediately upon filing pursuant to rule 485(b)
             [X]  on October __, 1998 pursuant to rule 485(b)          
             [ ]  60 days after filing pursuant to rule 485(a)(1)
             [ ]  on ___________ pursuant to rule 485(a)(1)
             [ ]  75 days after filing pursuant to rule 485(a)(2)
             [ ]  on ___________ pursuant to rule 485(a)(2).

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                                       2

<PAGE>
 

- --------------------------------------------------------------------------------
The definitive Prospectus and Statement Additional Information for the series of
the Registrant designated Acorn Fund, Acorn International and Acorn USA, dated 
May 1, 1998, were filed in post-effective amendment no. 61 to Registrant's 
registration statement, filed pursuant to Rule 485(b) of the Securities Act of 
1933, on April 30, 1998 (1933 Act No. 2-34223), and are incorporated herein by 
reference.
- --------------------------------------------------------------------------------
<PAGE>

 
Acorn Twenty

Acorn Foreign Forty
================================================================================

- --------------------------------------------------------------------------------

     Acorn Twenty invests for long-term capital growth. The Fund invests
primarily in the stocks of U.S. companies with market capitalizations of $1
billion to $10 billion. Acorn Twenty ordinarily focuses its investments in 20 to
25 U.S. companies.

- --------------------------------------------------------------------------------
    
     Acorn Foreign Forty invests for long-term capital growth. The Fund invests
primarily in the stocks of foreign companies with market capitalizations of $1
billion to $10 billion. The Fund ordinarily has investments in 40 to 60
companies in developed markets.     

- --------------------------------------------------------------------------------

     Please read this prospectus before investing, and keep it on file for
future reference. It contains important information, including how the Funds
invest and the services available to shareholders.
    
     A Statement of Additional Information (SAI) dated the date of this
prospectus, and any supplement to the SAI, has been filed with the Securities
and Exchange Commission (SEC), and is incorporated herein by reference (is
legally considered a part of this prospectus). The SAI is available free upon
request by calling Acorn at 1-800-9-ACORN-9 (1-800-922-6769). You may also
obtain the SAI, as well as other information that has been electronically filed,
from the SEC's web site (www.sec.gov).     

     Acorn Twenty and Acorn Foreign Forty are series of Acorn Investment Trust.

LIKE ALL MUTUAL FUNDS, THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY
THE SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION, NOR
HAS THE SECURITIES AND EXCHANGE COMMISSION OR ANY STATE SECURITIES COMMISSION
PASSED UPON THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY REPRESENTATION TO
THE CONTRARY IS A CRIMINAL OFFENSE.

    
The Acorn Family of Funds
100% No-Load Funds
  Acorn Twenty
  Acorn Foreign Forty

Acorn Investment Trust
227 West Monroe Street
Suite 3000
Chicago, Illinois 60606     

Prospectus and Account Application
October 15, 1998
<PAGE>
 

<TABLE>     
<CAPTION>
CONTENTS
================================================================================
<S>                                                                         <C>
The Funds at a Glance                                                          2
     .Goal & Strategy
     .Management and Organization
     .Who May Want to Invest                                                   3
     .Risks                         
     .Buying and Selling Shares     
                                    
Expenses and Performance                                                       4
     .Expenses                      
     .Performance                                                              5
 
Your Account                                                                   6
     .Doing Business with Acorn     
     .Choices for Your Account Registration                  
     .How to Buy Shares                                                        8
     .How to Sell Shares                                                       9
     .Selling Shares by Telephone                                             
     .Selling Shares in Writing
     .Signature Guarantee                                                     10
     .Redemption Price             
                                   
Shareholder and Account Policies                                              11
     .Statements and Reports       
     .Share Price                  
     .Purchases                                                               
     .Transactions with Dealers
     .Redemptions                                                             12
     .Address Changes                                                         13
     .Telephone Transactions
     .Telephone Exchange Plan and Money Market Funds                          14
     .Exchange Plan Restrictions                                              15
 
Dividends, Capital Gains, and Taxes                                           16
     .Distribution Options
     .Taxes
     .Foreign Income Taxes                                                    17
                                     
The Funds in Detail                                                           18
     .Organization
     .Management
     .Transfer Agent and Custodian                                            20
     .Distributor                    
     .Expenses                                                               
                                     
How the Funds Invest                                                          21
     .Acorn Twenty
     .Acorn Foreign Forty
     .General Information                                                     22
 
Securities, Investment Practices, and Risks                                   23
     .Common Stocks
     .Diversification
     .Foreign Securities                                                      
     .Managing Investment Exposure                                            25
     .Debt Securities                                                         26
     .Illiquid and Restricted Securities                                      27
     .Other Investment Companies                                              
     .Lending and Repurchase Agreements
     .When-Issued and Delayed Delivery Securities
 
Quick Reference Guide                                                         29
     .Account Forms                                                           
     .How to Buy Shares                                                       30
     .How to Sell Shares                                                      32
     .How to Contact Us                                                       34
</TABLE>      

                                       i
<PAGE>

THE FUNDS AT A GLANCE
================================================================================

Goal and Strategy
- --------------------------------------------------------------------------------

     Acorn Twenty invests for long-term capital growth. The Fund invests
primarily in the stocks of U.S. companies with market capitalizations of $1
billion to $10 billion. Acorn Twenty is a non-diversified fund that ordinarily
focuses its investments in 20 to 25 U.S. companies.

     Under normal market conditions, Acorn Twenty invests most of its assets in
common stocks, and securities exchangeable or convertible into common stocks of
U.S. companies, but may also invest in other types of securities.

- --------------------------------------------------------------------------------
    
     Acorn Foreign Forty invests for long-term capital growth. The Fund invests
primarily in the stocks of foreign companies with market capitalizations of $1
billion to $10 billion. The Fund is a non-diversified fund that ordinarily has
investments in 40 to 60 companies and invests in developed markets.

     Under normal market conditions, Acorn Foreign Forty invests most of its
total assets in equity securities, including common and preferred stocks,
warrants or other similar rights, and convertible securities. The Fund invests
in the common stocks of foreign companies in at least three developed countries,
but may also invest in other types of securities, including debt 
securities.     

Management and Organization
- --------------------------------------------------------------------------------

     The Funds are series of Acorn Investment Trust ("Acorn" or the "Trust").
Wanger Asset Management, L.P. (WAM), the Funds' investment adviser, employs a
team approach to management of the Funds. The management team consists of the
Funds' portfolio managers, other WAM portfolio managers, and research analysts.
Each team member has one or more areas of expertise, and shares responsibility
for providing ideas, information, and knowledge in managing the Funds. Daily
decisions on portfolio selection rest with the lead portfolio managers or co-
managers who utilize the input and advice of the management team in making
purchase and sale determinations. Ralph Wanger is the chief investment officer
of WAM, and lead strategist for all of the Acorn funds.
    
     Acorn Twenty. John H. Park and Mark H. Yost are the co-portfolio managers
of Acorn Twenty. Mr. Park is a vice president of the Trust and a principal of
WAM. He has been a member of WAM's investment management team since July 1993.
Mr. Yost is a vice president of the Trust and has been a member of WAM's
investment management team since October 1995.

     Acorn Foreign Forty. Marcel P. Houtzager is the lead-portfolio manager of
Acorn Foreign Forty. Mr. Houtzager is a vice president of the Trust and a
principal of WAM. He has been a member of WAM's investment management team since
1992.     
         
Who May Want to Invest
- --------------------------------------------------------------------------------

     The Funds are suitable for investors who are willing to hold their shares
through market fluctuations and the accompanying changes in share values. The
Funds are not appropriate investments for those seeking short-term price
appreciation or for "market-timers."

                                       1
<PAGE>
 

Risks
- --------------------------------------------------------------------------------
   
     Over time, stocks have shown greater growth potential than other types of
securities. In the short term, however, stock prices may fluctuate widely in
response to company, market, or economic news. Because they are non-diversified,
the Funds have the ability to take larger positions in a smaller number of
issuers. While WAM believes that a strategy of investing in a limited number of
securities has the potential for higher total returns than a strategy of
investing in a larger number of securities, this may increase the volatility of
the Funds' investment performance. Also, if the securities in which a Fund
invests perform poorly, the Fund could incur greater losses than it might have
had if it invested in a larger number of securities.

     The value of the Funds' investments and the returns it generates vary from
day to day. Performance depends on WAM's skills in identifying the trends that
are the basis for the Funds' stock selections, and in picking individual stocks,
as well as general market and economic conditions. When you sell your shares,
they may be worth more or less than you paid for them. The Funds are not, alone
or together, a balanced investment plan and there can be no assurance that the
Funds will achieve their investment objectives.     

Buying and Selling Shares
- --------------------------------------------------------------------------------

     The minimum initial investment in a Fund is $1,000 (lower for some IRAs).
You may buy shares directly from the Funds without payment of any sales charges.
There are no "12b-1" fees or redemption fees. To invest you must be a U.S.
resident with a social security or tax identification number.

     See "Your Account" for how to buy and sell shares.

                                       2
<PAGE>
 

EXPENSES AND PERFORMANCE
================================================================================

Expenses
- --------------------------------------------------------------------------------

     Transaction Expenses. Shareholder transaction expenses are charges you pay
when you buy or sell shares of the Funds:

     Maximum sales charge on purchases and
       reinvested dividends                           None
     Deferred sales charge on redemptions             None
     Redemption fee                                   None
     Exchange fee                                     None
     Wire transaction fee                             None

     Annual fund operating expenses. Each Fund pays its own operating expenses,
including the management fee to WAM. Expenses are factored into each Fund's
share price daily, and are not charged directly to shareholder accounts.

     The Funds expect to incur the following expenses, expressed as a percentage
of the Fund's average net assets: 

<TABLE>
<CAPTION>
                                                         Acorn Twenty   Acorn Foreign Forty
                                                         ------------   -------------------
<S>                                                      <C>            <C>
     Management Fee....................................     0.90%              0.95%
     12b-1 fee.........................................     None               None
     Other expenses
       Administration fee..............................     0.05               0.05
       Other operating expenses (after reimbursement)..     0.40               0.45
                                                            ----               ----
     Total operating expenses (after reimbursement)....     1.35%              1.45%
</TABLE>

     The purpose of the expense table is to help you understand the costs and
expenses of investing in the Funds. WAM has agreed to reimburse Acorn Twenty for
any ordinary operating expenses exceeding 1.35% of its average net assets, and
Acorn Foreign Forty for any ordinary operating expenses exceeding 1.45% of its
average net assets, over each fiscal year. Absent reimbursement, "Other
operating expenses" would be estimated to be 3.65% for Acorn Twenty, and 3.98%
for Acorn Foreign Forty. "Total operating expenses" absent reimbursement would
be estimated to be 4.60% for Acorn Twenty and 4.98% for Acorn Foreign Forty. The
estimate of "Other operating expenses" is based on the estimated expenses the
Funds expect to incur during their initial partial fiscal year ending December
31, 1998.
    
     .Example: Let's say, hypothetically, that a Fund's annual return is 5% and
that its operating expenses are exactly as shown on the previous page. For every
$1,000 you invested, here's how much you would have paid in total expenses if
you closed your Fund account after the number of years indicated:     

                                       3
<PAGE>

<TABLE>
<CAPTION>
                                              Acorn Twenty   Acorn Foreign Forty
                                              ------------   -------------------
<S>                                           <C>            <C>
After 1 year                                       $14              $15
After 3 years                                      $43              $46
</TABLE> 

     The purpose of the example is to illustrate the effect of expenses, but is
not meant to suggest actual or expected costs or returns, all of which may vary.
Because the Funds are new, the above amounts are estimates.

Performance
- --------------------------------------------------------------------------------

     Mutual fund performance is commonly measured as total return. Total return
is the change in value of an investment in a fund over a given period, assuming
reinvestment of all dividends and capital gains. Total return reflects actual
performance over a stated period of time. Average annual total return is a
hypothetical rate of return that, if achieved annually, would have produced the
same total return if performance had been constant over the entire period.
Average annual total returns smooth out variations in performance; they are not
the same as actual year-by-year results.

     Total returns are based on past results and are not a prediction of future
performance. They do not include the effect of income taxes.

     The Funds sometimes show their performance compared to stock indexes
(described in the SAI), or give their ratings or rankings determined by
unrelated organizations.

YOUR ACCOUNT
================================================================================

Doing Business with Acorn
- --------------------------------------------------------------------------------

     Acorn provides investors with service Monday through Friday, except
holidays, from 8:00 a.m. to 4:30 p.m. Central time.

     To reach Acorn, call:
    
     .For fund information, prices, or literature--1-800-9-ACORN-9
     (1-800-922-6769) (from outside the U.S. 1-312-634-9240).

     .To add to your existing account, redeem shares, or exchange shares by
     telephone--call our transfer agent at 1-800-962-1585 (outside the U.S. 
     1-617-328-5000 ext. 6457). See "Shareholder and Account Policies" for more
     information.

     .For help in setting up your account or for IRA assistance--call our
     transfer agent at 1-800-962-1585 (outside the U.S. 1-617-328-5000 ext.
     6457).     

                                       4
<PAGE>
 

     .For 24-hour account balances, 7 days a week--1-800-962-1585.

Choices for Your Account Registration
- --------------------------------------------------------------------------------

     Acorn will register your account in any of the ways described below.

     Individual or Joint Ownership
          For your general investment needs

     Individual accounts are owned by one person. Joint accounts can have two or
more owners.

     Accounts for Minors
          To invest for a minor's education or other future needs

     .Gift or Transfer to Minor (UGMA/UTMA) custodial accounts provide a way to
          give money to a minor. The Account Application must include the
          minor's social security number.
        
     .Education IRAs may be established on behalf of a beneficiary under age 18
          to save for his or her education. Distributions from an Education IRA
          are tax-free as long as the proceeds are used to pay for "qualified
          higher education expenses." Single taxpayers with income up to $95,000
          per year, and married couples with income up to $150,000 per year, are
          allowed to contribute up to $500 per year per beneficiary. The $500
          annual maximum contribution is subject to reduction if the
          contributor's income exceeds those amounts. Education IRAs are not
          available during the subscription period (October 20--November
          20).    

     Transfer on Death (TOD)
          To designate a beneficiary for your non-retirement account

     TOD registration enables you to designate an individual or entity to
     receive the proceeds of your fund account upon your death. TOD registration
     differs from a joint account--with TOD registration, the account owner
     retains full control over the disposition of shares held in the account
     during his or her lifetime, and may change or remove the beneficiary at any
     time without the consent of the beneficiary. TOD registration may not be
     available to residents of certain states. Call 1-800-962-1585 for more
     information.

     Trust or Established Employee Benefit or Profit-Sharing Plan
          For money being invested by a trust, employee benefit plan, or profit-
          sharing plan

     The trust or plan must be established before an account can be opened.

     Corporation or Other Entity
          For investment needs of corporations, associations, partnerships,
          institutions, or other groups

     You will need to send a certified corporate resolution with your Account
     Application.

     Retirement Plans
          To shelter your retirement savings from taxes

                                       5
<PAGE>
 
     Retirement plans allow individuals to shelter investment income and capital
     gains from current taxes. Contributions to these accounts may be tax-
     deductible. IRAs require a special application (call 1-800-962-1585).

     . Traditional IRAs allow anyone of legal age and under 70 1/2 with earned
          income to save up to $2,000 per tax year. If your spouse has less than
          $2,000 in earned income, he or she may still contribute up to $2,000
          to an IRA, as long as you and your spouse's combined earned income is
          at least $4,000.

     . Rollover IRAs retain special tax advantages for certain distributions
          from employer-sponsored retirement plans.
    
     . Roth IRAs allow single taxpayers with earned income up to $110,000 per
          year, and married couples with earned income up to $160,000 per year,
          to contribute up to $2,000, or $4,000, respectively, per year.
          Contributions to Roth IRAs are not tax-deductible, but withdrawals are
          not taxable if the Roth IRA has been held at least five years, and you
          are at least 59 1/2, disabled, or use the proceeds (up to $10,000) to
          purchase a first home.     

     . Simplified Employee Pension Plans (SEP-IRAs) allow small business owners
          or those with self-employment income to make tax-deductible
          contributions of up to 15% of the first $160,000 of compensation per
          year for themselves and any eligible employees.
   
     . SIMPLE-IRAs must be established by an employer (including a self-employed
          person), and enable all employees of the employer to elect to have up
          to $6,000 per year deducted from their paychecks on a before-tax basis
          and deposited directly into an account maintained for the individual
          employee. The employer is also generally required to make a
          contribution for each employee who elects to contribute.     

     . Other retirement plans--The Fund may be used as an investment in other
          kinds of retirement plans, including Keogh or corporate profit-sharing
          and money purchase plans, 403(b) plans, and 401(k) plans.  All of
          these accounts need to be established by the trustee of the plan.
          Acorn does not offer prototypes of these plans.

          For more information about the tax advantages and consequences of
          investing in any of these plans, please consult your tax adviser.

How to Buy Shares
- --------------------------------------------------------------------------------

     You can open a new account by:

     . mailing in an Account Application with your check or money order payable
     to "Acorn Twenty" or "Acorn Foreign Forty" for $1,000 or more (the Acorn
     funds do not accept third party checks, except for IRA rollover checks that
     are properly endorsed);

     . using the exchange plan to move $1,000 or more from an account with Acorn
     Fund, Acorn International, Acorn USA (each of which is a series of Acorn
     Investment Trust) or one of the Reich & Tang Funds into a new identically
     registered account in Acorn Twenty 

                                       6
<PAGE>
         
     or Acorn Foreign Forty. This option is not available during the
     subscription period (October 20 through November 20). See "Shareholder and
     Account Policies" for more exchange plan information; or

     . wire by calling 1-800-962-1585 to set up your account and to arrange a
     wire transaction. This option is not available during the subscription
     period (October 20 through November 20). Note: You may not need to submit a
     new Account Application if you are a current Acorn shareholder. When you
     call, a representative will assist you. Not available for IRA accounts.    

     After your account is open, you may add to it by:

     . wiring money from your bank;

     . moving money via ACH transfer from your bank account by telephone if you
     participate in the Telephone Purchase Plan (select this option on the
     Account Application or request a Doing Business with Acorn form to
     establish);

     . using the Telephone Exchange Plan to move your investment from another
     Acorn fund to Acorn Twenty or Acorn Foreign Forty, or from one of the Reich
     & Tang Funds;

     . using the Automatic Investment Plan to move money from your financial
     institution via ACH transfer to your Acorn Twenty or Acorn Foreign Forty
     account on a monthly or quarterly basis; or

     . mailing your check or money order payable to "Acorn Twenty" or "Acorn
     Foreign Forty" for $100 or more with the stub from one of your account
     statements, with a slip from the investment booklet provided by Acorn or
     with a letter of instruction.  The Acorn funds do not accept third party
     checks, except for IRA rollover checks that are properly endorsed.

     The Acorn funds use the Automated Clearing House (ACH) to transfer money to
and from your fund accounts and participating financial institutions.
Participants in the ACH network include banks, savings banks, brokerage houses,
money market funds, and credit unions which electronically process transactions
primarily through the Federal Reserve System.

     Your purchase money and your Account Application must both be received by
Closing Time (usually 3:00 p.m. Central time) for you to receive that day's
price. An order is considered received when the Account Application (for a new
account) or information identifying the account and the money are received by
Acorn's transfer agent, or by certain authorized agents, some of which may
charge a fee for their services. See "Shareholder and Account Policies--Share
Price" for information about share price and transactions with certain financial
services companies and broker-dealers. If the proceeds of your wire order are
received, but your Account Application has not been received, you will receive
the price for the day on which your Account Application is received. Your
Account Application must be received no later than 12:00 noon Central time the
day after your wire is received, or your wire will be returned to you.

     If you are investing through an Acorn IRA (any kind) for the first time you
will need a special application. Call 1-800-962-1585. For both initial and
subsequent IRA investments, please indicate the year for which the investment is
being made.

                                       7
<PAGE>
 
     Minimum Investments
   
<TABLE> 
     <S>                                       <C>
     To open an account                        $1,000
     To open a Traditional or Roth IRA         $1,000
     To add to an account                      $  100
</TABLE>     

     The Automatic Investment Plan allows you to request a transfer of money
(minimum $100; maximum $50,000) from your pre-designated bank account to your
fund account on a monthly or quarterly basis.  Quarterly investments will be
made in January, April, July, and October.  The money will be transferred on or
about the 15th of the month unless you designate a different day.  If the day
you selected falls on a Saturday, Sunday, holiday, or any other day on which the
NYSE is closed for trading, the transaction will be processed on the next
business day.  To participate in the Automatic Investment Plan, complete the
information on the Account Application or request a Doing Business with Acorn
form.

     If you sign up for the Automatic Investment Plan and later wish to change
the amount or frequency of your automatic investments, or stop future
investments, you may do so by calling us at 1-800-962-1585 at least one week
prior to your next scheduled investment date.

     More details about how to buy shares are in "A Quick Reference Guide" at
the back of this prospectus.

How to Sell Shares
- --------------------------------------------------------------------------------
   
     You can arrange to take money out of your fund account at any time by
selling (redeeming) some or all of your shares.  Your shares will be sold at the
NAV (share price) next calculated after your order is received and accepted.
See "Shareholder and Account Policies--Share Price" for more information about
share price and transactions with certain financial services companies and
broker-dealers.  To sell shares in a regular (non-IRA) account, you may use any
of the methods described here.  To sell shares in an Acorn IRA, your request
must be made in writing, except for exchanges between the Acorn funds or to the
Reich & Tang Short Term Income Fund Money Market Portfolio, which can be
requested by calling 1-800-962-1585.  If you need an IRA Withdrawal Request
form, call us at 1-800-9-ACORN-9 (1-800-922-6769).    

Selling Shares by Telephone
- --------------------------------------------------------------------------------

     The Telephone Redemption Plan lets you redeem $100 to $50,000 per day by
phone. You must make your telephone redemptions by Closing Time to receive that
day's NAV.  Transaction requests received after Closing Time will receive the
NAV next calculated after receipt of the request.  You automatically have the
Telephone Redemption Plan unless you decline it on your Account Application. If
you have changed the address on your account by telephone within 60 days of the
telephone redemption request, this service is not available. Instead, you must
send a letter of instruction signed by all account owners with the signatures
guaranteed.  See "Signature Guarantee."

     The Systematic Withdrawal Plan lets you establish automatic monthly or
quarterly 

                                       8
<PAGE>
 
redemptions from your account in specified dollar amounts if you have a $25,000
minimum Acorn account balance. If you wish to establish this feature, call 
1-800-9-ACORN-9 (1-800-922-6769) for a Doing Business with Acorn form.

     More details about how to sell shares are in "A Quick Reference Guide" at
the back of this prospectus.

Selling Shares in Writing
- --------------------------------------------------------------------------------

     Write a letter of instruction including:

     . your name,

     . the fund's name,

     . your fund account number,

     . the dollar amount or number of shares to be redeemed,

     . the stock certificates representing your shares to be redeemed, if you
     hold certificates for your shares, and

     . any other applicable requirements listed under "A Quick Reference Guide
     How to Sell Shares."

     Mail your letter to:

     State Street Bank and Trust Co.
     Attn: Acorn Family of Funds
     P.O. Box 8502
     Boston, MA 02266-8502

     If you are using overnight mail:

     Boston Financial Data Services
     Attn: Acorn Family of Funds
     66 Brooks Drive
     Braintree, MA 02184
     1-617-328-5000 ext. 6457

     DO NOT SIGN YOUR STOCK CERTIFICATES. Send them by registered or certified
mail so that you may receive a confirmation of delivery.

Signature Guarantee
- --------------------------------------------------------------------------------

     Certain requests must include a signature guarantee, designed to protect
you and Acorn from fraudulent activities. Your request must be made in writing
and include a signature guarantee if any of the following situations applies:

     . you wish to redeem more than $50,000 worth of shares;

                                       9
<PAGE>
 
     . your name has changed by marriage or court order (complete a Changing
     Your Account Registration form or send a letter indicating your account
     number(s) and old and new names, signing the letter in both the old and new
     names and having both signatures guaranteed);

     . you wish to establish TOD registration on an existing account or change a
     TOD beneficiary (see "Your Account--Choices for Your Account
     Registration");

     . your address has changed within the last 60 days and you would like to
     redeem shares;

     . the check is being mailed to an address different from the one on your
     account (address of record);

     . the check is being made payable to someone other than the account owner;
     or

     . you are instructing us to wire the proceeds to a bank or brokerage
     account and have not signed up for the Telephone Redemption Plan.

     You should be able to obtain a signature guarantee from a bank, broker-
dealer, credit union (if authorized under state law), securities exchange or
association, clearing agency, or savings association.  A notary public cannot
provide a signature guarantee.

Redemption Price
- --------------------------------------------------------------------------------

     The price at which your shares will be redeemed is determined by the time
of day Acorn's transfer agent, or another authorized agent, receives your
redemption request.

     Closing Time is the close of New York Stock Exchange (NYSE) regular session
trading, which is usually 3:00 p.m. Central time but is sometimes earlier.

     To get today's price--

     . Use the Telephone Redemption Plan to call your redemption request in
     before Closing Time (note that the Closing Time to exchange out of the
     Reich & Tang Funds is 11:00 a.m. Central time).

     . Have your written redemption request, with a signature guarantee, if
     required, and any supporting documents, delivered to Acorn's transfer
     agent, or another authorized agent, before Closing Time.

SHAREHOLDER AND ACCOUNT POLICIES
================================================================================

Statements and Reports
- --------------------------------------------------------------------------------

Statements and reports that Acorn sends to you include:

     . Confirmation statements (after every transaction in your account or
     change in your account registration), excluding automatic investment plan
     purchases, which are confirmed on a quarterly consolidated account
     statement. Automatic Investment Plan accounts using the 15th of each month
     (or the 15th of the first month of each quarter) as the investment

                                       10
<PAGE>
 
     date may also have purchases confirmed monthly instead of just quarterly.
     Call 1-800-962-1585 to request this service.

     . Quarterly and year-end consolidated account statements

     . Shareholder reports

     If you would like us to send duplicate statements to someone, simply call
us at 1-800-962-1585, and we can take your request over the telephone.  Average
cost statements for shares redeemed are available upon request for most
accounts.

     If you need copies of your historical account information, please call 
1-800-962-1585. There is a small charge for historical account information for
prior years.

Share Price
- --------------------------------------------------------------------------------
   
     The Funds are open for business each day the NYSE is open. The offering
price (price to buy one share) and redemption price (price to sell one share)
are the fund's net asset value (NAV) calculated each day at Closing Time.
Closing Time is the time of the close of regular session trading on the NYSE,
which is usually 3:00 p.m. Central time but is sometimes earlier.

     A Fund's NAV is the value of a single share. The NAV is computed by adding
up the value of the Fund's investments, cash, and other assets, subtracting its
liabilities, and then dividing the result by the number of shares
outstanding.    

     Each Fund's portfolio securities and assets are valued primarily on the
basis of market quotations from the primary market in which they are traded or,
if quotations are not readily available, by a method that the board of trustees
believes accurately reflects a fair value.  Values of foreign securities are
translated from the local currency into U.S. dollars using current exchange
rates.  Because of the different trading hours in various foreign markets, the
calculation of NAV does not take place at the same time as the determination of
the prices of many foreign securities held by the Funds.  Those timing
differences may have a significant effect on a Fund's NAV.

     Your purchase or redemption of Fund shares will be priced at the NAV next
calculated after your investment (including the Account Application, if for a
new account, and the money) or redemption request is received by Acorn's
transfer agent, or by certain other agents and dealers authorized to accept
purchase and redemption requests on Acorn's behalf.  An order received before
Closing Time will get that day's price.  Telephone orders received after Closing
Time will be processed at the NAV next calculated after receipt of the order.

Purchases
- --------------------------------------------------------------------------------

     . All of your purchases must be made in U.S. dollars and checks must be
     drawn on U.S. banks. Acorn does not accept third party checks, except for
     IRA rollover checks that are properly endorsed.

     . Acorn does not accept cash, credit cards, or credit card checks.

                                      11
<PAGE>
 
     . If payment for your check or telephone purchase order does not clear,
     your purchase will be canceled and you will be liable for any losses or
     fees the fund or its transfer agent incurs.

     . Your Automatic Investment Plan and Telephone Purchase Plan may be
     immediately terminated if any item is unpaid by your financial institution.
    
     . When you make a purchase by telephone, the money is ordinarily drawn from
     your bank account the day after you call.  Fund shares are purchased at the
     NAV calculated the day after you call.  See "Share Price."      

     Acorn reserves the right to reject any specific purchase order, including
certain purchases through the exchange plan. See "Exchange Plan Restrictions."
A purchase may be refused if, in WAM's opinion, it would disrupt management of
the Funds or would not be in the best interests of a Fund's existing
shareholders.

Transactions with Dealers
- --------------------------------------------------------------------------------

     You may purchase or redeem shares of a Fund through investment dealers,
banks, or other financial institutions.  Certain financial institutions that
have entered into sales agreements with Acorn may enter confirmed purchase
orders or redemption requests on behalf of customers on an expedited basis,
including orders by phone, with payment to follow no later than the time when
the Funds are priced on the following business day.  If payment is not received
by that time, the financial institution could be held liable for resulting fees
or losses.  These institutions may charge for their services or place
limitations on the extent to which you may use the services offered by Acorn.
Any such charges could constitute a substantial portion of a smaller account and
may not be in your best interest.  There are no charges or limitations imposed
by Acorn other than those described in this prospectus if shares are purchased
(or redeemed) directly from Acorn.

     Acorn may from time to time authorize certain financial services companies,
broker-dealers or their designees ("authorized agents") to accept purchase,
redemption, and exchange requests from their clients on whose behalf the
authorized agent holds shares of the Funds.  For purchase orders placed through
an authorized agent, a shareholder will pay a Fund's NAV next computed after the
receipt by the authorized agent of such purchase order, plus any applicable
transaction charge imposed by the agent.  For redemption orders placed through
an authorized agent, a shareholder will receive redemption proceeds which
reflect the NAV next computed after the receipt by the authorized agent of the
redemption order, less any redemption fees imposed by the agent.  Some financial
institutions that act as Acorn's agent or that otherwise maintain nominee
accounts with the Funds for their clients for whom they hold fund shares might
not charge any transaction fees directly to investors in the Funds.  However,
such companies may charge a fee (usually a percentage of the average net assets
held in such accounts) for accounting, shareholder servicing, and distribution
services the institution provides with respect to the underlying fund shares.
WAM pays any such fees.

Redemptions
- --------------------------------------------------------------------------------

     . Normally, redemption proceeds will be mailed within seven days after your
     redemption request is received by Acorn's transfer agent or another
     authorized agent.

     . Redemption checks are made payable to the shareholders of record; if you
     wish for the 

                                       12
<PAGE>
 
     check to be made payable to someone other than the account owners, you must
     submit your request in writing, and the signatures of all shareholders of
     record must be guaranteed. See "Your Account--Signature Guarantee."

     . Each Fund may hold payment on redemptions until it is reasonably
     satisfied that it has received payment for a recent purchase made by check,
     by the Automatic Investment Plan, or by the Telephone Purchase Plan, which
     can take up to 15 days.

     . If you elected to participate in the Telephone Redemption Plan, Acorn can
     send payment for your redemption to your bank account by wire or ACH
     transfer. Your bank may impose a fee for the incoming wire. Payment by wire
     is usually credited to your bank account on the next business day after
     your call.

     . Redemptions may be suspended or payment dates postponed on days when the
     NYSE is closed (other than weekends or holidays), when trading on the NYSE
     is restricted, or as permitted by the SEC.

     . Certain accounts (such as trust accounts, corporate accounts, and
     custodial accounts) may require documentation in addition to the redemption
     request. Call 1-800-962-1585 for more information.

     If the value of your account falls below $1,000 because of redemptions,
Acorn reserves the right to close your account and send the proceeds to you.
Your shares will be redeemed at the NAV calculated on the day your account is
closed.

     If checks representing (1) redemption proceeds, (2) withdrawals under a
systematic withdrawal plan, or (3) dividend and capital gains distributions are
returned "undeliverable" or remain uncashed for six months, the checks will be
canceled and the proceeds will be reinvested in the Fund issuing the check at
the NAV on the date of cancellation. In addition, after such six-month period,
(1) your systematic withdrawal plan will automatically be canceled and future
withdrawals will occur only when requested, or (2) your cash election will
automatically be changed and future dividends and distributions will be
reinvested.

Address Changes
- --------------------------------------------------------------------------------

     You may change your address over a recorded line by calling 1-800-962-1585.
Acorn will send a written confirmation of the change to both your old and new
addresses. No telephone redemptions may be made for 60 days after a change of
address by phone. During those 60 days, a signature guarantee will be required
for any written redemption request unless your change of address was made in
writing with a signature guarantee.

Telephone Transactions
- --------------------------------------------------------------------------------

     You may initiate many transactions by telephone.

     Transactions over a recorded line (1-800-962-1585):

     . Change your address;

     . Request duplicate statements to be sent to someone you designate;

                                       13
<PAGE>
 
     . Request an average cost statement for shares redeemed (available for most
     accounts);

     . Request a current account statement;

     . Purchase shares through the Telephone Purchase Plan (plan must be pre-
     established);

     . Redeem $50,000 or less and request a wire or ACH transfer to your bank
     account (bank account information must be pre-designated on your fund
     account registration; not available for IRA accounts);

     . Change the frequency or amount, or discontinue the Automatic Investment
     Plan on your account(s);

     . Add or discontinue the Telephone Exchange Plan to your account;

     . Add or discontinue the Telephone Redemption Plan to your account;

     . Add the Automatic Exchange Plan to your account (to exchange between one
     Acorn fund and another each month or quarter);

     . Change your distribution option, not including the cash payment via ACH
     option (does not apply to IRA accounts);

     . Redeem $50,000 or less, with a check mailed to the address of record
     (does not apply to IRA accounts, and your address of record must not have
     changed within the last 60 days);

     . Exchange money from a non-IRA individual account to an existing IRA
     account with an identical registration;

     . Exchange money between identically registered accounts in Acorn Twenty,
     Acorn Foreign Forty, Acorn Fund, Acorn International, Acorn USA, or certain
     Reich & Tang Funds, or exchange money from one fund to establish an
     identically registered account in another fund;

     . Change the contribution year on an IRA account to the previous year up
     until April 15 of the following year; and

     . Copy the account options on your account to other identically registered
     accounts.

     Acorn will not be responsible for any loss resulting from unauthorized
transactions if it follows reasonable procedures designed to verify the identity
of the caller.  Those procedures may include recording the call, requesting
additional information, and sending written confirmation of telephone
transactions.

     You should verify the accuracy of telephone transactions immediately upon
receipt of your confirmation statement. If you do not want to be able to
purchase or redeem shares by telephone, decline these privileges on your Account
Application or call Acorn for instructions at 1-800-962-1585.

     If you are unable to reach Acorn by phone (for example, during periods of
unusual market 

                                       14
<PAGE>
 
activity), consider placing your order by mail.

Telephone Exchange Plan and Money Market Funds
- --------------------------------------------------------------------------------

     Acorn's Telephone Exchange Plan permits you to exchange your investment
between one Acorn fund and another, or between an Acorn fund and one of the
money market mutual funds participating in the plan (Reich & Tang Funds) upon
telephone instructions.

Money Funds

     The following Reich & Tang Funds are available under the Telephone Exchange
Plan: Short Term Income Fund, Money Market Portfolio; Short Term Income Fund,
U.S. Government Portfolio; Daily Tax Free Income Fund; California Daily Tax Free
Income Fund; Connecticut Daily Tax Free Income Fund; Florida Daily Municipal
Income Fund; Michigan Daily Tax Free Income Fund; New Jersey Daily Municipal
Income Fund; New York Daily Tax Free Income Fund; North Carolina Daily Municipal
Income Fund; and Pennsylvania Daily Municipal Income Fund.

     Each of the Reich & Tang Funds is a no-load fund managed by Reich & Tang
Asset Management, L.P. and offers check writing privileges (for accounts other
than IRAs) in addition to the Exchange Plan. Only Short Term Income Fund, Money
Market Portfolio is available for IRA accounts.

     The price at which shares are exchanged is determined by the time of day
your request is received. To get today's price:

   . For an IRA account, call us at 1-800-962-1585 before Closing Time.

   . If you are exchanging from one Acorn fund into another, or into one of the
   Reich & Tang Funds, call us at 1-800-962-1585 before Closing Time.

   . If you are exchanging from one of the Reich & Tang Funds to one of the
   Acorn funds, call Reich & Tang at 1-800-221-3079 before 11:00 a.m. Central
   time.

     If your call is received after the times noted above, your exchange will be
processed at the NAV next calculated after receipt of your call.

     Because of the time needed to transfer money between the Acorn funds and
the Reich & Tang Funds, you may not exchange into and out of a Reich & Tang Fund
on the same or successive days; there must be at least one day between
exchanges.

Exchange Plan Restrictions
- --------------------------------------------------------------------------------

     . Generally, you will be limited to 4 round trip exchanges per year (a
     round trip is an exchange out of one fund into another fund, and then back
     again).

     . Shares of the fund you are exchanging into must be available for sale in
     your state.

     . You may only exchange between accounts that are registered in the same
     name, address, and taxpayer identification number.

                                       15
<PAGE>
 
     . If you are opening a new account by exchange, your exchange must be at
     least $1,000.
        
     . The Exchange Plan is not available for shares of a Fund for which you
     have been issued certificates. (If you want to exchange shares between
     funds, call 1-800-962-1585 to get instructions for returning your
     certificates.)    

     . If your account is subject to backup withholding, you may not use the
     Exchange Plan.

     . Because excessive trading can hurt fund performance and shareholders,
     Acorn reserves the right to temporarily or permanently terminate the
     exchange privilege of any investor who makes excessive use of the Exchange
     Plan.

     . Acorn also reserves the right to refuse exchange purchases by any person
     or group, if Acorn believes the purchase will be harmful to existing
     shareholders.

     . Before exchanging into a fund, you should read its prospectus. Call 
     1-800-922-6769 for a prospectus.

     . Exchanges may have tax consequences for you.

     Acorn reserves the right to terminate or modify the Exchange Plan at any
time, but will try to give you prior notice whenever they are reasonably able to
do so.

DIVIDENDS, CAPITAL GAINS AND TAXES
================================================================================

     Each Fund distributes substantially all of its net income and net realized
capital gains to shareholders each year.  Normally, dividends are paid in June
and December, and capital gains are distributed in December.

Distribution Options
- --------------------------------------------------------------------------------

     When you open an account, specify on your Account Application how you would
like to receive your distributions.  If you ever want to change your
distribution option, call us at 1-800-962-1585.  The Fund offers three options:

     . Reinvestment Option.  Both your dividends and capital gain distributions
     will be automatically reinvested in additional shares of your Fund.  If you
     do not indicate a choice on your Account Application, you will be assigned
     this option.

     . Income-Only Option. Your capital gain distributions will be automatically
     reinvested, but you may receive a check for each dividend, or have the
     proceeds sent to your pre-designated financial institution via ACH
     transfer.

     . Cash Option.  You will be sent a check for each dividend and capital gain
     distribution or you may have the proceeds sent to your pre-designated bank
     account via ACH transfer.

     For IRA accounts, all distributions are automatically reinvested because
payment of distributions in cash would be a taxable distribution from your IRA,
and might be subject to income tax penalties if you are under 59 1/2 years old.
After you are 59 1/2, you may request payment of distributions in cash.

                                       16
<PAGE>
 
     When you reinvest, the reinvestment price is the Fund's NAV at Closing Time
on the reinvestment date. The mailing of distribution checks will usually begin
on the payment date, which is usually one week after the ex-dividend date. The
ex-dividend date is the day after the record date.

Taxes
- --------------------------------------------------------------------------------

     As with any investment, you should consider how your investment in a Fund
will be taxed. If your account is a tax-deferred or tax-exempt account (for
example, an IRA or an employee benefit plan account), the following tax
discussion does not apply. If your account is not tax-deferred or tax-exempt,
however, you should be aware of the following tax rules:
    
     Taxes on distributions.  Distributions are subject to federal income tax,
and may also be subject to state or local taxes.  Your distributions are taxable
when they are paid, whether you take them in cash or reinvest them in additional
shares. However, distributions declared in October, November or December and
paid in January are taxable as if they were paid on December 31.

     For federal tax purposes, income and short-term capital gain distributions
are taxed as dividends and long-term capital gain distributions are taxed as
long-term capital gains. Every January, Acorn will send you and the IRS a
statement, called a Form 1099-DIV, showing the amount of each taxable
distribution you received in the previous year. A year-end tax guide will
accompany your Form 1099. You may not receive a Form 1099 if the total
distributions you received for the year are less than $10.00.     

     Taxes on transactions.  Your redemptions--including exchanges between funds
or into a money fund--are subject to capital gains tax. A capital gain or loss
is the difference between the cost of your shares and the price you receive when
you sell them.

     Whenever you sell shares of a Fund, Acorn will send you a confirmation
statement showing how many shares you sold and at what price.  You will also
receive a year-end statement every January.  Acorn sends you an average cost
statement for shares you redeemed to assist you or your tax preparer.  It is up
to you or your tax preparer to determine whether any given sale resulted in a
capital gain and, if so, the amount of tax to be paid.  Be sure to keep your
regular account statements; the information they contain will be essential in
calculating the amount of your capital gains.

Foreign Income Taxes
- --------------------------------------------------------------------------------

     Investment income received by a Fund from sources within foreign countries
may be subject to foreign income taxes at the source.  If a Fund pays
nonrefundable taxes to foreign governments during the year, the taxes will
reduce that Fund's dividends but will still be included in your taxable income.
You may be able to claim an offsetting credit or deduction on your tax return
for your share of foreign taxes paid by Acorn Foreign Forty (but not Acorn
Twenty because not enough of Acorn Twenty's assets are invested in foreign
securities for Acorn Twenty to be able to pass through the foreign tax credit).
Acorn Foreign Forty will send you this information along with your annual Form
1099-DIV and year-end tax guide.

     When you sign your Account Application, you will be asked to certify that
your social 

                                       17
<PAGE>
 
security or taxpayer identification number is correct and that you are not
subject to 31% backup withholding for failing to report income to the IRS. If
you violate IRS regulations, the IRS can require Acorn to withhold 31% of your
taxable distributions and redemptions.

THE FUNDS IN DETAIL
================================================================================

Organization
- --------------------------------------------------------------------------------
    
     Acorn Twenty and Acorn Foreign Forty are each series of Acorn Investment
Trust ("Acorn" or the "Trust"), an open-end, management investment company. The
Trust is a Massachusetts business trust organized on April 21, 1992. The other
series of the Trust are Acorn Fund, Acorn International, and Acorn USA.      

     Each share of a Fund is entitled to participate pro rata in any dividends
and other distributions declared by the board of trustees with respect to the
Fund, and all shares of the Fund have equal rights in the event of liquidation
of the Fund.

     The Trust is governed by a board of trustees, which is responsible for
protecting the interests of the shareholders of the Acorn funds. The trustees
are experienced executives and professionals who meet at regular intervals to
oversee the activities of the Trust. A majority of the trustees are independent
of WAM.

     Acorn may hold special meetings of shareholders to elect or remove
trustees, change fundamental policies, approve a management contract, or for
other purposes. Acorn will mail proxy materials in advance, including a voting
card and information about the proposals to be voted on. You are entitled to one
vote for each share of a Fund and any other Acorn fund that you own.
Shareholders not attending these meetings are encouraged to vote by proxy.

Management
- --------------------------------------------------------------------------------

     The Funds are managed by Wanger Asset Management, L.P. (WAM), 227 West
Monroe Street, Suite 3000, Chicago, Illinois 60606; WAM chooses the Funds'
investments and handles their business affairs, under the direction of the board
of trustees. WAM is a limited partnership managed by its general partner, Wanger
Asset Management, Ltd. WAM manages more than $6 billion in assets.
        
    
     WAM employs a team approach to management of the Funds. The management team
is made up of the lead portfolio manager or co-managers, other WAM portfolio
managers and research analysts. Team members share responsibility for providing
ideas, information and knowledge in managing the funds, with each team member
having one or more particular areas of expertise applicable to the management of
the Funds. Daily decisions on portfolio selection rest with the lead portfolio
managers or co-portfolio managers who utilize the input and advice of the     

                                      18
<PAGE>
 
management team in making purchase and sale determinations.
   
     WAM is also the investment advisor to the other series of the Trust--Acorn
Fund, Acorn International and Acorn USA. Each of those funds is a small- to mid-
cap growth fund. Those funds generally invest in companies with a total stock
market capitalization of less than $1 billion. Initially, they buy small
companies, then hold them as they grow to become mid- and large-size companies.
Those funds are offered by a separate prospectus. Call 1-800-9-ACORN-9 for more
information.    

     Ralph Wanger is the president of the Trust and chief investment officer of
WAM.  He has been involved in managing all of the Acorn funds since each fund
began.  Mr. Wanger has been a member of the board of Acorn (and its predecessor,
The Acorn Fund, Inc.) since 1970, and is a principal of WAM.  Mr. Wanger is
primarily responsible for development of the investment strategies followed by
each of the Acorn funds.
   
     John H. Park and Mark H. Yost are the co-portfolio managers of Acorn
Twenty. Mr. Park is a vice president of the Trust and a principal of WAM. He has
been a member of WAM's investment management team since July 1993. Mr. Park
received his Chartered Financial Analyst (CFA) designation in 1996 and earned
both his undergraduate and M.B.A. degrees from the University of Chicago.    
    
     Mr. Yost is a vice president of the Trust and has been a member of WAM's
investment management team since October 1995. Mr. Yost has been co-portfolio
manager of Wanger U.S. Smaller Companies Fund, an investment company offering
shares to investors outside the U.S., since its inception on June 23, 1997. Mr.
Yost is also the portfolio manager of the WAM Yost Partnership, L.P., a smaller
company focused limited partnership. Before joining WAM, Mr. Yost was an
investment analyst for First Chicago Corporation. Mr. Yost received his CFA
designation in 1996. Mr. Yost received his B.A. from St. Olaf College and his
M.B.A. from the University of Chicago.      
    
   Marcel P. Houtzager is the lead portfolio manager of Acorn Foreign Forty.
Mr. Houtzager is a vice president of the Trust and a principal of WAM. He has
been a member of WAM's investment management team since 1992. Mr. Houtzager is
the lead portfolio manager of Wanger International Small Cap Advisor, a mutual
fund investing in small cap stocks outside the U.S. Mr. Houtzager received his
CFA designation in 1996 and is a Certified Public Accountant. He received his
B.A. from Pomona College in 1983 and his M.B.A. from the University of
California at Berkeley in 1985.

     The other officers of WAM are:

     Leah J. Zell is a vice president of the Trust and a principal of WAM.  She
has been analyzing international securities for Acorn Fund since 1984, and Acorn
International since 1992. Ms. Zell is lead portfolio manager of Acorn
International, a mutual fund investing in smaller foreign companies with assets
at September 30, 1998 of more than $1.8 billion. Ms. Zell received her CFA
designation in 1987. She earned her undergraduate degree from Radcliffe College
and holds a Ph.D. from Harvard University.     

     Since June 23, 1997, Mr. Houtzager and Ms. Zell have co-managed the Wanger
European Smaller Companies Fund, an investment company offering shares to
investors outside the United States.
    
     Charles P. McQuaid is a co-portfolio manager of Acorn Fund.  Mr. McQuaid
has contributed to Acorn Fund's growth since 1978.  He is a senior vice
president of Acorn Investment Trust and a member of its board of trustees.  Mr.
McQuaid is a principal and the Director of Research at WAM.  A CFA, he earned 
his B.B.A. from the University of Massachusetts and his M.B.A from the
University of Chicago.

     Robert A. Mohn is the lead portfolio manager of Acorn USA.  Mr. Mohn is a
vice president of Acorn Investment Trust and a principal of WAM.  In addition to
being lead manager of      

                                       19
<PAGE>

     
Acorn USA, Mr. Mohn is also a member of WAM's management team for Acorn Fund,
which he joined in 1992. He is a CFA and received his undergraduate degree from
Stanford University and his M.B.A. from the University of Chicago.

     Howard L. Kastel is the chief executive officer and president of Wanger
Asset Management.  he is also a principal of WAM.  Prior to working in his
current position, Mr. Kastel was a partner with the Chicago law firm McDermott,
Will & Emery, where he served as a long time legal counsel to WAM.  In addition
to his unique inside knowledge of WAM, he has years of long-range strategic
planning experience.  As a litigator and counsel for a number of top-drawer
corporations such as Grant Thornton, he has served as chief advisor to major
financial, professional, and manufacturing institutions since 1972. Mr. Kastel
earned his B.A. from Harvard University and his J.D. degree from Loyola
University School of Law (Chicago).

     Merrillyn J. Kosier, senior vice president and secretary, and Bruce H.
Lauer, vice president and treasurer, are the other executive officers of Acorn.
Ms. Kosier is the director of marketing and shareholder services at WAM and Mr.
Lauer is chief administrative officer Before joining WAM, Ms. Kosier was vice
president of marketing and Mr. Lauer was first vice president of investment
accounting for Kemper Financial Services.     

Transfer Agent and Custodian
- --------------------------------------------------------------------------------

     State Street Bank and Trust Company ("State Street") is the Funds' transfer
agent and custodian.
    
     The smooth operation of the Funds depends on the ability of State Street
and the other service providers to the Funds to provide those services without
interruption.  Some computer systems used today are unable to process date-
related information because they are not programmed to distinguish between the
year 2000 and the year 1900.  WAM, like many other businesses, is taking steps
to ensure that the computer systems on which the smooth operation of the Funds
depends will continue to function properly.  WAM is working with the service
providers to the Funds, such as State Street and various broker-dealers through
which portfolio securities of the Funds are traded, to arrange for testing of
internal and external systems.  Based on the information currently available,
WAM does not anticipate any material impact on the delivery of services
currently provided.  There can be no assurance, however, that the steps taken by
WAM in preparation for the year 2000 will be sufficient to avoid any adverse
impact on the Funds.      

Distributor
- --------------------------------------------------------------------------------

     Shares of the Funds are offered for sale through WAM Brokerage Services,
L.L.C. (WAM BD) without any sales commission or charges to the Funds or their
shareholders. WAM BD is wholly-owned by WAM, the Funds' investment advisor, and
the investment advisor's general partner, Wanger Asset Management, Ltd. WAM BD's
address is 227 West Monroe Street, Suite 3000, Chicago, Illinois 60606. All
distribution expenses relating to the Funds are paid by WAM, including the
payment or reimbursement of any expenses incurred by WAM BD.

Expenses
- --------------------------------------------------------------------------------

     Like all mutual funds, each Fund pays expenses related to its daily
operations. Expenses paid out of a Fund's assets are reflected in its share
price or dividends.  Each Fund pays 

                                       20
<PAGE>
 
management and administration fees to WAM for managing its investments and
business affairs. See "Expenses and Performance." For services furnished by WAM,
Acorn Twenty pays an annual management fee of 0.90% of its average daily net
assets. Acorn Foreign Forty pays an annual management fee of 0.95% of its
average daily net assets.
   
     While the management fee is a significant component of each Fund's annual
operating costs, the Funds have other expenses as well.  The Funds have a
separate administrative services agreement with WAM under which WAM receives a
fee, calculated daily and paid monthly, at the annual rate of 0.05 of 1% of its
average daily net assets.  The Funds pay the cost of custodial, stock transfer,
dividend disbursing, audit and legal services, and membership in trade
organizations.  They also pay other expenses such as the cost of maintaining the
registration of their shares under federal law, complying with state securities
laws, proxy solicitations, printing and distributing notices and copies of the
prospectus and shareholder reports furnished to existing shareholders, taxes,
insurance premiums, and the fees of trustees not affiliated with WAM.    

HOW THE FUNDS INVEST
================================================================================

     Acorn Twenty and Acorn Foreign Forty seek long-term growth of capital.  The
investment philosophy and strategy of each of the Funds is discussed in the
following paragraphs.

Acorn Twenty
- --------------------------------------------------------------------------------

     Acorn Twenty invests primarily in the stocks of U.S. companies with market
capitalizations of $1 billion to $10 billion.  Acorn Twenty is a non-diversified
fund that ordinarily focuses its investments in 20 to 25 U.S. companies.

     Under normal market conditions, Acorn Twenty invests most of its assets in
common stocks, and securities exchangeable or convertible into common stocks, of
U.S. companies, but may also invest in other types of securities.  The Fund may
invest up to 15% of its total assets in foreign securities.  Generally, the Fund
will invest in the securities of a foreign-based company only if its operations
are primarily located in the United States.

     Like all the Acorn funds, Acorn Twenty looks for high quality companies.
As a long-term investor, the Fund expects that its portfolio turnover rate will
not ordinarily exceed 50% annually.

Acorn Foreign Forty
- --------------------------------------------------------------------------------

     Acorn Foreign Forty invests primarily in the stocks of foreign companies
with market capitalizations of $1 billion to $10 billion.  The Fund is a non-
diversified fund that ordinarily has investments in 40 to 60 companies in
developed markets.
    
     Under normal market conditions, Acorn Foreign Forty invests at least 85% of
its total assets in equity securities of foreign companies, including common and
preferred stocks, warrants or other similar rights, and convertible securities,
but may also invest in any other type of security, including debt securities.
The Fund ordinarily invests in at least three developed countries.  The Fund may
invest up to 15% of its total assets in the securities of U.S. companies.
Generally, the Fund invests in a U.S. company only if its operations are
primarily located outside the United States.      

                                       21
<PAGE>
 
     Like all the Acorn funds, Acorn Foreign Forty looks for high quality
companies.  As a long-term investor, the Fund expects that its portfolio
turnover rate will not ordinarily exceed 50% annually.

Looking for high quality companies
- --------------------------------------------------------------------------------

     Acorn Twenty and Acorn Foreign Forty look for quality businesses, with each
investment ideally resting on a solid tripod of growth potential, financial
strength, and fundamental value.  The emphasis on fundamentals in relation to
price sets the Funds apart from pure "growth" or "value" funds.  Not all of the
companies in which the Funds invest necessarily have all of these
characteristics.

     The sources of growth are a growing marketplace for the company's product,
good design, efficient manufacturing, sound marketing, and good profit margins.
Financial strength means low debt, adequate working capital, and conservative
accounting principles.  Strong capitalization gives management the stability and
flexibility to reach strategic objectives.  Fundamental value means low relative
price.  The existence of a good company does not necessarily make its stock a
good buy.  The price of the stock determines value as measured relative to
dividends, earnings, cash flow, growth rate, book value, and economic
replacement value of assets.  Sometimes, value is found in a "special
situation."  A special situation arises when WAM believes the securities of a
particular company have been overlooked or undervalued by other investors in
connection with a significant change or development affecting the company's
business, and will, within a reasonable time, appreciate in value regardless of
general business conditions or movements of the market as a whole.  Developments
creating special situations might include, among others, the following:
liquidations, reorganizations, recapitalizations or mergers; material
litigation; technological breakthroughs; and new management or management
policies.  Although investing in securities of special situation companies
offers the potential for above-average returns, if the anticipated development
does not occur or produce the expected results, the value of those securities
may decline.

     WAM also believes that finding and understanding high quality companies is
important to reduce taxes and transaction costs.  In managing the Funds, WAM
tries to reduce these costs by investing with a long-term time horizon (at least
2-5 years) and avoiding frequent turnover of the stocks held by the Funds.
Occasionally, however, securities purchased on a long-term basis may be sold
within 12 months after purchase in light of a change in the circumstances of a
particular company or industry, or in general market or economic conditions.

General Information
- --------------------------------------------------------------------------------
   
     Each Fund may invest without limit in corporate or government obligations
or hold cash or cash equivalents if WAM determines that a temporary defensive
position is advisable. If investments in foreign securities appear to be
relatively unattractive because of current or anticipated adverse political or
economic conditions, Acorn Foreign Forty may hold cash or invest any portion of
its assets in securities of the U.S. government and equity and debt securities
of U.S. companies, as a temporary defensive measure. The Funds use various
techniques to increase or decrease their exposure to the effects of possible
changes in security prices, currency exchange rates, or other factors that
affect the value of their portfolios. These techniques may include buying and
selling options, futures contracts, or options on futures contracts, or entering
into currency exchange contracts or swap agreements.    

                                       22
<PAGE>
 

     The investment objective of each Fund is not fundamental and may be changed
by the board of trustees without shareholder approval. If there were such a
change, you should consider whether a Fund would remain an appropriate
investment in light of your then current financial position and needs. The Funds
are not intended, alone or together, to present a balanced investment program.

SECURITIES, INVESTMENT PRACTICES, AND RISKS
================================================================================

     The following pages contain more detailed information about types of
investments each Fund may make, and strategies WAM may employ in pursuit of each
Fund's investment objective, including information about the associated risks
and restrictions. All policies stated throughout this prospectus, other than
those identified as fundamental, can be changed without shareholder approval. A
complete statement of the Fund's investment restrictions is included in the SAI.
Policies and limitations are considered at the time of purchase; the sale of an
investment is not required because of a subsequent change in circumstances.

     WAM may not buy all of these instruments or use all of these techniques to
the fullest extent permitted, unless it believes that doing so will help the
Fund achieve its goal.

Common stocks
- --------------------------------------------------------------------------------

     The Funds invest mostly in common stocks, which represent an equity
interest (ownership) in a corporation. This ownership interest often gives the
Funds the right to vote on measures affecting the company's organization and
operations. The Funds also invest in other types of equity securities, including
preferred stocks and securities convertible into common stocks. Over time,
common stocks have historically provided superior long-term capital growth
potential. However, stock prices may decline over short or even extended
periods. Stock markets tend to move in cycles, with periods of rising stock
prices and periods of falling stock prices. As a result, the Funds should be
considered long-term investments, designed to provide the best results when held
for several years or more. The Funds may not be suitable investments if you have
a short-term investment horizon or are unwilling to accept fluctuations in share
price, including significant declines over a given period.

Diversification
- --------------------------------------------------------------------------------
   
     Diversification is a means of reducing risk by investing in a broad range
of stocks or other securities. Because they are non-diversified, the Funds have
the ability to take larger positions in a smaller number of issuers. The
appreciation or depreciation of a single stock may have a greater impact on the
NAV of a non-diversified fund, because the fund is likely to have a greater
percentage of its assets invested in that stock. As a result, each Fund's share
price can be expected to fluctuate more than that of broadly diversified funds
investing in similar securities. Because they are non-diversified, the Funds are
not subject to the limitations under the Investment Company Act of 1940 in the
percentage of their assets that they may invest in any one issuer. Both Funds
however, intend to comply with the diversification standards for regulated
investment companies under Subchapter M of the Internal Revenue Code (summarized
below under "Restrictions").    

     Restrictions:

     .    A Fund may not acquire securities of any one issuer, which at the time
of investment (a) represent more than 10% of the voting securities of the issuer
or (b) have a value greater than

                                      23
<PAGE>
 

10% of the value of the outstanding securities of the issuer;

     .    With respect to 50% of its total assets, a Fund may not purchase the
securities of any issuer (other than cash items and U.S. government securities
and securities of other investment companies) if such purchase would cause the
Fund's holdings of that issuer to exceed 5% of the Fund's total assets.

     .    A Fund may not invest more than 25% of its total assets in a single
issuer (other than U.S. government securities); and

     .    A Fund will not invest more than 25% of its total assets in the
securities of companies in a single industry (excluding U.S. government
securities).*

Foreign Securities
- --------------------------------------------------------------------------------

     Acorn Foreign Forty invests primarily in foreign securities. International
investing allows you to take advantage of changes in foreign economies and
market conditions. From time to time, many foreign economies have grown faster
than the U.S. economy, and the returns on investments in these countries have
exceeded those of similar U.S. investments. During other periods, however, some
foreign markets have declined, and there can be no assurance that a country's
economy will remain stable or more favorable than the U.S. economy.

     Investments in foreign securities provide opportunities different from
those available in the U.S., and risks which in some ways may be greater than in
U.S. investments, including: fluctuations in exchange rates of foreign
currencies; imposition of exchange control regulations or currency restrictions
that would prevent cash from being brought to the United States; less public
information with respect to issuers of securities; less governmental supervision
of stock exchanges, securities brokers, and issuers of securities; lack of
uniform accounting, auditing, and financial reporting standards; lack of uniform
settlement periods and trading practices; less liquidity, frequently greater
price volatility, and higher transaction costs in foreign markets than in the
United States; possible imposition of foreign taxes; possible investments in
securities of developing as well as developed countries; and sometimes less
advantageous legal, operational, and financial protections applicable to foreign
sub-custodial arrangements. Investing in countries outside the U.S. also
involves political risk. A foreign government might restrict investments by
foreigners, expropriate assets, seize or nationalize foreign bank deposits or
other assets, establish exchange controls, or enact other policies that could
affect investment in these nations. Economies in individual markets may differ
favorably or unfavorably from the U.S. economy in such respects as growth of
gross domestic product, rates of inflation, currency depreciation, capital
reinvestment, resource self-sufficiency, and balance of payments positions.
    
     Acorn Twenty may invest no more than 15% of its total assets in foreign
securities and will generally invest in a foreign-based company only if that
company's operations are primarily located in the United States. Acorn Twenty's
foreign investments, if any, will be in developed markets.     

     The Funds may invest from time to time in securities of foreign issuers
directly or in the

- --------------------
* These restrictions are "fundamental," which means that they cannot be changed
  without shareholder approval.

                                      24
<PAGE>
 
    
form of American Depositary Receipts (ADRs), European Depositary Receipts
(EDRs), Global Depositary Receipts (GDRs) or other securities representing
underlying shares of foreign issuers. Positions in these securities are not
necessarily denominated in the same currency as the common stocks into which
they may be converted. ADRs are receipts typically issued by an American bank or
trust company evidencing ownership of the underlying securities. EDRs are
European receipts evidencing a similar arrangement. GDRs are traded in U.S. and
non-U.S. markets.

     The Funds may invest in both "sponsored" and "unsponsored" depositary
receipts. In a sponsored depositary receipt, the issuer typically pays some or
all of the expenses of the depository and agrees to provide its regular
shareholder communications to receipt holders. An unsponsored depositary receipt
is created independently of the issuer of the underlying security. The receipt
holders generally pay the expenses of the depository and do not have an
undertaking from the issuer of the underlying security to furnish shareholder
communications. Each Fund may invest in depositary receipts that are not
sponsored by the issuer of the underlying security. To the extent a Fund does
so, it would probably bear its proportionate share of the expenses of the
depository and might have greater difficulty in receiving copies of the issuer's
shareholder communications than would be the case with a sponsored depositary
receipt.     

    
     Several European countries, including Austria, Belgium, Finland, France, 
Germany, Ireland, Italy, Luxembourg, the Netherlands, Portugal and Spain, 
adopted a single, uniform currency known as the "euro," effective January 1, 
1999. The euro conversion could have potential adverse effects on the Funds' 
ability to value their portfolio holdings in foreign securities, and could 
increase the costs associated with the Funds' operations. The Trust and WAM are 
working with the providers of services to the Funds in the areas of clearance 
and settlement of trades in an effort to avoid any material impact on the Funds 
due to the euro conversion; there can be no assurance, however, that the steps 
taken by the Trust or WAM will be sufficient to avoid any adverse impact on the 
Funds.      

     Restrictions:
   
     .    Under normal market conditions, Acorn Foreign Forty invests at least
85% of its total assets in equity securities of foreign companies. The Fund
ordinarily has investments in at least three developed countries.
 
     .    Acorn Twenty may invest up to 15% of its total assets in foreign
securities. Acorn Twenty's foreign investments are generally in companies whose
operations are primarily in the U.S.     

Managing Investment Exposure
- --------------------------------------------------------------------------------

     The Funds use various techniques to increase or decrease their exposure to
the effects of possible changes in security prices, currency exchange rates or
other factors that affect the value of the Funds' portfolios. These techniques
include buying and selling options, futures contracts, or options on futures
contracts, entering into currency exchange contracts or swap agreements, or
selling securities short against the box.

     These techniques are used by WAM to adjust the risk and return
characteristics of the Funds' portfolios. If WAM judges market conditions
incorrectly or employs a strategy that does not correlate well with the Funds'
investments, or if the counterparty to the transaction does not perform as
promised, the transaction could result in a loss. Use of these techniques may
increase the volatility of a Fund and may involve a small investment of cash
relative to the magnitude of the risk assumed. These techniques are used by the
Funds for hedging, risk management, or portfolio management purposes and are not
used for speculation.

     Currency exchange transactions. A currency exchange transaction may be
conducted either on a spot (i.e., cash) basis at the spot rate for purchasing or
selling currency prevailing in the foreign exchange market or through a forward
foreign currency contract ("forward contract"). A forward contract is an
agreement to purchase or sell a specified currency at a specified future date

                                      25
<PAGE>
 

(or within a specified time period) and price set at the time of the contract.
Forward contracts are usually entered into with banks, foreign exchange dealers,
or broker-dealers, are not exchange-traded, and are usually for less than one
year, but may be renewed.

     Currency exchange transactions may involve currencies of the different
countries in which the Funds may invest, and serve as hedges against possible
variations in the exchange rate between these currencies. The Funds' currency
transactions are limited to transaction hedging and portfolio hedging involving
either specific transactions or actual or anticipated portfolio positions.
Transaction hedging is the purchase or sale of a forward contract with respect
to a specific receivable or payable of a Fund accruing in connection with the
purchase or sale of portfolio securities. Portfolio hedging is the use of a
forward contract with respect to an actual or anticipated portfolio security
position denominated or quoted in a particular currency. The Funds may engage in
portfolio hedging with respect to the currency of a particular country in
amounts approximating actual or anticipated positions in securities denominated
in that currency. When the Funds own or anticipate owning securities in
countries whose currencies are linked, WAM may aggregate those positions as to
the currency hedged. Although forward contracts may be used to protect the Funds
from adverse currency movements, the use of such hedges may reduce or eliminate
the potentially positive effect of currency revaluations on the Fund's total
return.

     Options and futures. Each Fund may enter into stock index or currency
futures contracts (or options thereon) to hedge a portion of its portfolio, to
provide an efficient means of regulating its exposure to the equity markets, or
as a hedge against changes in prevailing levels of currency exchange rates. Each
Fund may write covered call options and purchase put and call options on foreign
currencies, securities, and stock indices. Futures contracts and options can be
highly volatile. A Fund's attempt to use such investments for hedging purposes
may not be successful and could result in reduction of that Fund's total return.

     Short sales against the box. Each Fund may make short sales of securities
if, at all times when a short position is open, the Fund owns an equal amount of
such securities or securities convertible into or exchangeable for, without
payment of any further consideration, securities of the same issue as, and equal
in amount to, the securities sold short. This technique is called selling short
"against the box." Selling short against the box may protect the Fund against
the risk of losses in the value of the portfolio securities sold short because
losses on the securities sold short should be wholly or partially offset by
gains in the short position (although this also means that the Fund would be
giving up the opportunity for gain).

     Restrictions:

     .    A Fund will not use futures contracts for speculation, and will limit
its use of futures contracts so that no more than 5% of its total assets would
be committed to initial margin deposits or premiums on such contracts.

     .    The aggregate market value of each Fund's currencies or portfolio
securities covering call or put options will not exceed 10% of that Fund's net
assets.

Debt Securities
- --------------------------------------------------------------------------------

     Bonds and other debt instruments are methods for an issuer to borrow money
from investors. The issuer pays the investor a fixed or variable rate of
interest, and must repay the

                                      26
<PAGE>
 

amount borrowed at maturity. Debt securities have varying degrees of quality and
varying levels of sensitivity to changes in interest rates.

     "Investment grade" debt securities are those rated within the four highest
ratings categories of Standard & Poor's Corporation ("S&P") or Moody's Investors
Services, Inc. ("Moody's") or, if unrated, determined by WAM to be of comparable
quality. Securities rated BBB or Baa are considered to be medium-grade and to
have speculative characteristics. Investment in non-investment grade debt
securities is speculative and involves a high degree of risk.

     Lower-rated debt securities (commonly called "junk bonds") are often
considered speculative and involve greater risk of default or price changes due
to changes in the issuer's creditworthiness. The market prices of these
securities may fluctuate more than higher-rated securities and may decline
significantly in periods of general economic difficulty.

     Money market instruments are high-quality, short-term debt securities that
present minimal credit risk. These instruments may carry fixed or variable
interest rates.

     Each Fund may invest without limit in corporate or government obligations,
or hold cash or cash equivalents if WAM determines that a temporary defensive
position is advisable. If investments in foreign securities appear to be
relatively unattractive because of current or anticipated adverse political or
economic conditions, Acorn Foreign Forty may hold cash or invest any portion of
its assets in securities of the U.S. government and equity and debt securities
of U.S. companies, as a temporary defensive measure. To meet liquidity needs
(which, under normal market conditions, are not expected to exceed 25% of total
assets) or for temporary defensive purposes, each Fund may hold cash in domestic
and foreign currencies and may invest in domestic and foreign money market
securities.

     Restrictions:

     .    There are no restrictions on the ratings of debt securities in which
the Funds may invest.

     .    Neither Fund intends to invest more than 20% of its total assets in
debt securities, nor more than 5% of its total assets in debt securities rated
at or lower than the lowest investment grade.

Illiquid and Restricted Securities
- --------------------------------------------------------------------------------

     Some investments may be determined by WAM to be illiquid, which means that
they may be difficult to sell promptly at an acceptable price. Other securities,
such as securities acquired in private placements, may be sold only pursuant to
certain legal restrictions. Difficulty in selling securities may result in
delays or a loss, or may be costly to the Funds.

     Restrictions:

     .    Neither Fund may purchase a security if, as a result, more than 15% of
its net assets would be invested in illiquid or restricted securities.

                                      27
<PAGE>
 
Other Investment Companies
- --------------------------------------------------------------------------------

     The Funds may invest from time to time in shares of other mutual funds and
other types of investment companies.  Investment in another investment company
may involve the payment of a premium above the value of the issuer's portfolio
securities, and is subject to market availability.  In the case of a purchase of
shares of such a company in a public offering, the purchase price may include an
underwriting spread.  As a shareholder in an investment company, a Fund would
bear its ratable share of that investment company's expenses, including its
advisory and administration fees. At the same time, the Fund would continue to
pay its own management fees and other expenses.  Neither Fund intends to invest
in such circumstances unless, in the judgment of WAM, the potential benefits of
such investment justify the payment of any applicable premium or sales charge,
and the additional layer of expense.

     Restrictions:
     ------------ 

     .    Each Fund generally may invest up to 10% of its assets in shares of 
other investment companies and up to 5% of its assets in any one investment
company (in each case measured at the time of investment). No investment in
another investment company may represent more than 3% of the outstanding voting
stock of the acquired investment company at the time of investment.

Lending and Repurchase Agreements
- --------------------------------------------------------------------------------

     A Fund generally may not make loans, but each Fund has the power to invest
in repurchase agreements and reverse repurchase agreements (generally as a cash
management technique).  A repurchase agreement involves a sale of securities to
a Fund in which the seller agrees to repurchase the securities at a higher
price, which includes an amount representing interest on the purchase price,
within a specified time. In the event of a bankruptcy of the seller, the Fund
could experience both losses and delays in liquidating its collateral.

     Restrictions:
     ------------ 

     .    A Fund may generally not make loans, but may (a) invest in debt 
securities within the limits described in the prospectus and SAI, (b) invest in
repurchase agreements, or (c) lend up to 33% of its portfolio securities.*
    
When-Issued and Delayed Delivery Securities
- --------------------------------------------------------------------------------

     Each Fund may invest in securities purchased on a when-issued or delayed
delivery basis. Although the payment terms of such a security are established at
the time a Fund enters into the commitment, the security may be delivered and
paid for a month or more after the date of purchase, when its value may have
changed.  A Fund will make such commitments only with the intention of actually
acquiring the securities, but may sell the securities before settlement date if
WAM considers it advisable for investment reasons.      

- ---------------------
*   These restrictions are "fundamental," which means that they cannot be
    changed without shareholder approval.

                                       28
<PAGE>
 
    
QUICK REFERENCE GUIDE

Account Forms
================================================================================

From time to time you may find it necessary to make changes to your account
privileges or registration. The following easy-to-use shareholder forms are
available upon request by calling 1-800-9-ACORN-9 (1-800-922-6769):

     To accomplish this:                   Please request this form:

     For changes to account services       .Doing Business with Acorn

     For re-registering your current       .Changing Your Account Registration
     account

     For re-registering your Acorn         .Broker-Dealer Transfer Form
     shares held by a broker to an
     account with Acorn

     For changes to your IRA               .Change of Beneficiary
     beneficiary designations

     For transferring money from           .IRA Transfer Form
     an IRA account with another
     institution to Acorn

     For redeeming shares from your        .IRA Withdrawal Form
     IRA account

     For adding or deleting accounts       .Consolidated Account Statement
     to/from your Consolidated             Maintenance Form
     Account Statement
     

                                      29
<PAGE>
 
    
     .QUICK REFERENCE GUIDE      

How to Buy Shares
- --------------------------------------------------------------------------------

Mail

               To open an account:

     . Complete and sign the Account Application. Make your check payable to
       "Acorn Twenty" or "Acorn Foreign Forty."

               Mail to the address on the Account Application, or for overnight
               delivery:

     Boston Financial Data Services
     Attn: Acorn Family of Funds
     66 Brooks Drive
     Braintree, MA 02184
     1-617-328-5000 ext. 6457

     . Acorn does not accept third party checks, except properly endorsed IRA
     rollover checks.

               To add to an account:
    
     . Make your check payable to "Acorn Twenty" or "Acorn Foreign Forty." Put
     your fund account number on your check.     

               Use the return envelope that comes with your statements, or mail
               to the address on your statement.

     . Acorn does not accept third party checks, except properly endorsed IRA
     rollover checks.

Telephone: 1-800-962-1585

               To open an account:

     . You generally may not open a new account by telephone; however, you may
               open a new account by faxing your Account Application to us and
               wiring your purchase money. Note: You may not need to submit a
               new Account Application if you are a current Acorn shareholder.
               When you call, a representative will assist you. See "Your
               Account--How to Buy Shares."

     . Exchange between the Acorn funds, or from a Reich & Tang Fund account
               with the same registration, including name, address, and taxpayer
               ID number.

               To add to an account:

     . Exchange between accounts with the same registration, including name,
               address, and taxpayer ID number.

                                      30
<PAGE>
 

     . Use the Telephone Purchase Plan to transfer $100 to $50,000 from your
               bank account. Call first to verify that this service is in place
               on your account. (This service is not available for IRAs.)
    
Wire     

               To open an account:

     . Call 1-800-962-1585 to set up your account and to arrange a wire
               transaction. Note: You may not need to submit a new Account
               Application if you are a current Acorn shareholder. When you
               call, a representative will assist you. (This service is not
               available for IRA accounts.)

               To add to an account:

     . Wire to:

     State Street Bank & Trust Co.
     Attn: Mutual Funds
     Boston, MA 02110
     Routing #0110-0002-8
     Deposit DDA 9902-990-2
    
     Specify "Acorn Twenty" or "Acorn Foreign Forty," the account name, and the
               account number.     

     Minimum wire amount: $100.
    
     TDD Service for the deaf and hearing impaired: 1-800-306-4567.     

Automatic Investment Plan

               To open an account:

     . You may not open a new account through the Automatic Investment Plan.

               To add to an account:

     . Sign up on the Account Application for monthly or quarterly transfers of
     $100 to $50,000 from your bank account, or call 1-800-9-ACORN-9
     (1-800-922-6769) for a Doing Business with Acorn form to establish this on
     your account. If you already have this service, you can easily change the
     frequency or amount of your automatic investments over the telephone by
     calling 1-800-962-1585.

     TDD service for the deaf and hearing-impaired: 1-800-306-4567

How to Sell Shares
- --------------------------------------------------------------------------------

Telephone 1-800-962-1585

               All accounts types, except IRAs:

                                      31
<PAGE>
 

     . To verify that the Telephone Redemption Plan is in place, call 1-800-962-
     1585. You automatically have this feature on your new account unless you
     tell us that you do not want it. To receive redemption proceeds via ACH
     transfer, complete the information on the Account Application or request a
     Doing Business with Acorn form to establish this on your account.

     . Minimum: $100; maximum: $50,000;

     All account types:

     . To exchange between identically registered accounts:

     . You must make your telephone redemptions by Closing Time (usually 3:00
     p.m. Central time) to receive that day's price.

Mail

     Individuals, Joint Owners, Sole Proprietorships, UGMA, UTMA

     . The letter of instruction must be signed by all persons required to sign
     for transactions (usually, all owners of the account), exactly as their
     names appear on the account.

     IRAs

     . The account owner should complete an IRA Withdrawal Request form. Call 
     1-800-9-ACORN-9 (1-800-962-1585) to request this form.

     Trust

     . The trustee(s) must sign the letter indicating capacity as trustee(s). If
     the account registration does not include the name of the trustee(s),
     provide a copy of the trust document certified within the last 60 days.

     Business or Organization

     . The person(s) authorized by the corporate resolution to act on the
     account must sign, in that person's official capacity, and the redemption
     request must be on corporate letterhead.

     . If redeeming more than $50,000, include a corporate resolution certified
     within 60 days and a letter of instruction with the signature guaranteed.

     Executor, Administrator, Conservator, Guardian

     . Call 1-800-962-1585 for instructions.

Wire

     All account types, except IRAs

     . You must sign up for payment of redemptions by wire before using this
     feature. Call to verify that this service is in place--1-800-962-1585.

                                      32
<PAGE>
 
     . Minimum wire: $1,000; maximum: $50,000.

     . Minimum ACH transfer:  $100; maximum: $50,000

     . You must make your telephone redemptions by Closing Time (usually 3:00
     p.m. Central time) to receive that day's price.
    
     TDD Service for the deaf and hearing impaired: 1-800-306-4567.      

Automatic Exchange

     All account types

     . Call 1-800-962-1585 to set up monthly or quarterly automatic exchanges of
     $100 to $50,000 between identically registered accounts. Your automatic
     exchange will occur on or about the 15th day of each month unless you
     designate a different day (if quarterly, in January, April, July and
     October).

     TDD service for the deaf and hearing-impaired: 1-800-306-4567

     Note: Some redemptions require signature guarantees. Please see the
information under "Your Account--Signature Guarantee."

How to Contact Us
- --------------------------------------------------------------------------------

Mail

     . for regular mail delivery, including purchases, written exchanges,
     redemptions, and IRA contributions:

     State Street Bank & Trust Co.
     Attn: Acorn Family of Funds
     P. O. Box 8502
     Boston, MA 02266-8502

     . for overnight deliveries of purchases, written exchanges, redemptions, or
     IRA contributions

     Boston Financial Data Services
     Attn: Acorn Family of Funds
     66 Brooks Drive
     Braintree, MA 02184

     . the Funds' advisor

     Wanger Asset Management, L.P.
     227 W. Monroe St., Suite 3000
     Chicago, IL 60606-5016

     . the Funds' distributor

                                       33
<PAGE>
 
     WAM Brokerage Services, L.L.C.
     227 W. Monroe St., Suite 3000
     Chicago, IL 60606-5016

Telephone

     . for Fund information, literature, prices, and performance information 
     1-800-9-ACORN-9 (1-800-922-6769) (from outside the U.S. 1-312-634-9240)
 
     . for account balances, telephone purchases, exchanges and redemptions, and
     for IRA information 1-800-962-1585 (from outside the U.S.: 1-617-328-5000
     ext. 6457)

     . to exchange out of a money fund 1-800-221-3079

     . TDD service for the deaf and hearing impaired 1-800-306-4567

     Customer service is available on business days from 8:00 a.m. to 4:30 p.m.
Central time.
    
Internet      

     Web site: www.wanger.com
     E-mail: [email protected]

Wire

     . to wire money from your bank to add to an existing account

     State Street Bank & Trust Co.
     Attn: Mutual Funds
     Boston, MA 02110
     Routing #0110-0002-8
     Deposit DDA 9902-990-2

     Specify "Acorn Twenty" or "Acorn Foreign Forty" and the name and the number
of your account.

                                       34
<PAGE>
 
 . The Acorn Family of Funds

 . Trustees

  Irving B. Harris
  Chairman

  James H. Lorie
  Vice Chairman

  Leo A. Guthart

  Jerome Kahn, Jr.

  David C. Kleinman
 
  Charles P. McQuaid

  Roger S. Meler

  Adolph Meyer, Jr.

  Ralph Wanger


 . Officers

  Ralph Wanger
  President

  Marcel P. Houtzager
  Vice President

  Kenneth A. Kalina
  Assistant Treasurer

  Merrillyn J. Kosler
  Senior Vice President and Secretary

  Bruce H. Lauer
  Vice President and Treasurer

  Charles P. McQuaid
  Senior Vice President

  Robert A. Mohn
  Vice President

  John H. Park
  Vice President

  Mark H. Yost
  Vice President

  Leah J. Zell
  Vice President

 . Investment Advisor
  Wanger Asset Management, L.P.
  
  227 West Monroe Street, Suite 3000
  
  Chicago, Illinois 60606
  
  1-800-9-ACORN-9
 
  (1-800-922-6769)

  e-mail: [email protected]
 
  web site: www.wanger.com or
            www.acomfunds.com


 . Distributor 

  WAM Brokerage Services, L.L.C.

  227 West Monroe Street

  Suite 3000

  Chicago, Illinois 60606
  

 . Transfer Agent, Dividend Disbursing

  Agent and Custodian

  State Street Bank and Trust Company

  Attention: Acorn Family of Funds

  P.O. Box 8502

  Boston, Massachusetts 02266-8502

  1-800-962-1585
 
 . Legal Counsel

  Bell, Boyd & Lloyd

  Chicago, Illinois


 . Independent Auditors

  Ernst & Young LLP

  Chicago, Illinois

                                      35
<PAGE>
 
                                 Acorn Twenty
                              Acorn Foreign Forty
                              Subscription Offer

     Through November 20, 1998, shares of Acorn Twenty and Acorn Foreign Forty
(each, a "Fund," and together, the "Funds") are being offered by subscription.
Subscribing for Fund shares allows you to reserve shares that will be issued by
that Fund on November 23, 1998 at the initial offering price (net asset value)
of $10.00 per share. You can subscribe by sending in your completed and signed
purchase application, along with your check. Your check will be held, uncashed,
until November 23, 1998, the date the Funds will begin operations and your
account will be opened. There can be no assurance that either Fund's net asset
value after the close of the Subscription Period will be more than $10.00 per
share.


<PAGE>
 
ACORN INVESTMENT TRUST                                    227 West Monroe Street
STATEMENT OF ADDITIONAL INFORMATION                                   Suite 3000
October 15, 1998                                         Chicago, Illinois 60606
                                                                 1-800-9-ACORN-9
                                                                (1-800-922-6769)
<TABLE> 
<CAPTION> 

ACORN TWENTY
ACORN FOREIGN FORTY

No-Load Funds

- --------------------------------------------------------------------------------
                               TABLE OF CONTENTS
                               -----------------
                                                                           Page
                                                                           ----
<S>                                                                       <C> 
Information About the Funds...................................................1
Investment Objectives and Policies............................................2
Investment Techniques and Risks...............................................2
Performance Information......................................................21
Investment Adviser...........................................................22
Distributor..................................................................23
The Trust....................................................................23
Trustees and Officers........................................................24
Purchasing and Redeeming Shares..............................................27
Additional Tax Information...................................................29
Portfolio Transactions.......................................................30
Custodian....................................................................31
Independent Auditors.........................................................32
Appendix - Description of Bond Ratings.......................................33

- --------------------------------------------------------------------------------
</TABLE> 

     This Statement of Additional Information ("SAI") is not a prospectus but
provides information that should be read in conjunction with the prospectus of
Acorn Twenty and Acorn Foreign Forty (each, a "Fund," together, the "Funds")
dated the date of this SAI and any supplement thereto, which may be obtained
from Acorn at no charge by writing or telephoning Acorn at its address or
telephone number shown above.

                          Information About the Funds

     Acorn Twenty invests primarily in the stocks of U.S. companies with market
capitalizations of $1 billion to $10 billion. Acorn Twenty is a non-diversified
fund that ordinarily focuses its investments in 20 to 25 U.S. companies.
    
     Acorn Foreign Forty invests for long-term capital growth. The Fund invests
primarily in the stocks of foreign companies with market capitalizations of $1
billion to $10 billion. The Fund is a non-diversified fund that ordinarily has
investments in 40 to 60 companies in developed markets.      
<PAGE>
 
     The Funds are non-diversified under the federal securities laws. However,
the Funds comply with the diversification standards established by the tax laws.
See "Investment Techniques and Risks Diversification" for more information.

     The Funds are series of Acorn Investment Trust ("Acorn" or the "Trust").
The discussion below supplements the description in the prospectus of the Funds'
investment objectives, policies, and restrictions. For information about any of
the other Acorn funds, request a copy of that fund's prospectus and SAI, which
may be obtained free of charge by writing or telephoning Acorn at its address or
telephone number shown on the cover page of this SAI.

                       Investment Objectives and Policies

     The Funds invest with the objective of long-term growth of capital. The
Funds are not, alone or together, a balanced investment program, and there can
be no assurance that either Fund will achieve its investment objective.

     The Funds use the techniques and invest in the types of securities
described below and in the prospectus.

                        Investment Techniques and Risks

Common Stocks

     The Funds invest mostly in common stocks, which represent an equity
interest (ownership) in a corporation. This ownership interest often gives the
Funds the right to vote on measures affecting the company's organization and
operations. The Funds also invest in other types of equity securities, including
preferred stocks and securities convertible into common stocks. Over time,
common stocks have historically provided superior long-term capital growth
potential. However, stock prices may decline over short or even extended
periods. Stock markets tend to move in cycles, with periods of rising stock
prices and periods of falling stock prices. As a result, the Funds should be
considered long-term investments, designed to provide the best results when held
for several years or more. The Funds may not be suitable investments if you have
a short-term investment horizon or are unwilling to accept fluctuations in share
price, including significant declines over a given period.

Diversification

      is a means of reducing risk by investing in a broad range
of stocks or other securities. Because they are non-diversified, the Funds have
the ability to take larger positions in a smaller number of issuers. The
appreciation or depreciation of a single stock may have a greater impact on the
NAV of a non-diversified fund, because it is likely to have a greater percentage
of its assets invested in that stock. As a result, each Fund's share price can
be expected to fluctuate more than that of broadly diversified funds investing
in similar securities. Because they are non-diversified, the Funds are not
subject to the limitations under the Investment Company Act of 1940 in the
percentage of their assets that they may invest in any one issuer. Both Funds
however, intend to comply with the diversification standards for

                                       2
<PAGE>
 
regulated investment companies under Subchapter M of the Internal Revenue Code
(summarized below under "Investment Restrictions").

Foreign Securities

     The Funds invest in foreign securities, which may entail a greater degree
of risk (including risks relating to exchange rate fluctuations, tax provisions,
or expropriation of assets) than does investment in securities of domestic
issuers. Under normal market conditions, Acorn Foreign Forty invests at least
85% of its total assets in foreign securities; Acorn Twenty investments in
foreign securities are limited to not more than 15% of its total assets.
    
     The Funds may invest in securities of foreign issuers directly or in the
form of American Depositary Receipts (ADRs), European Depositary Receipts
(EDRs), Global Depositary Receipts (GDRs) or other securities representing
underlying shares of foreign issuers. Positions in these securities are not
necessarily denominated in the same currency as the common stocks into which
they may be converted. ADRs are receipts typically issued by an American bank or
trust company evidencing ownership of the underlying securities. EDRs are
European receipts evidencing a similar arrangement. GDRs trade in both U.S. and
non-U.S. markets. Generally ADRs, in registered form, are designed for use in
the U.S. securities markets and EDRs, in bearer form, are designed for use in
European securities markets. The Funds may invest in both "sponsored" and
"unsponsored" depositary receipts. In a sponsored depositary receipt, the issuer
typically pays some or all of the expenses of the depository and agrees to
provide its regular shareholder communications to depositary receipt holders. An
unsponsored depositary receipt is created independently of the issuer of the
underlying security. The depositary receipt holders generally pay the expenses
of the depository and do not have an undertaking from the issuer of the
underlying security to furnish shareholder communications. Therefore, in the
case of an unsponsored depositary receipt, a Fund is likely to bear its
proportionate share of the expenses of the depository and it may have greater
difficulty in receiving shareholder communications than it would have with a
sponsored depositary receipt. Neither Fund expects to invest 5% or more of its
total assets in unsponsored depositary receipts.     

     The Funds' investment performance is affected by the strength or weakness
of the U.S. dollar against the currencies of the foreign markets in which its
securities trade or in which they are denominated. For example, if the dollar
falls in value relative to the Japanese yen, the dollar value of a yen-
denominated stock held in the portfolio will rise even though the price of the
stock remains unchanged. Conversely, if the dollar rises in value relative to
the yen, the dollar value of the yen-denominated stock will fall. (See
discussion of transaction hedging and portfolio hedging under "Currency Exchange
Transactions," below.)

     Investors should understand and consider carefully the risks involved in
foreign investing. Investing in foreign securities, positions in which are
generally denominated in foreign currencies, and utilization of forward foreign
currency exchange contracts involve risks and opportunities not typically
associated with investing in U.S. securities. These considerations include:
fluctuations in exchange rates of foreign currencies; possible imposition of
exchange control regulation or currency restrictions that would prevent cash
from being brought back to the United States; less public information with
respect to issuers of securities; less governmental

                                       3
<PAGE>
 
supervision of stock exchanges, securities brokers, and issuers of securities;
lack of uniform accounting, auditing, and financial reporting standards; lack of
uniform settlement periods and trading practices; less liquidity and frequently
greater price volatility in foreign markets than in the United States; possible
imposition of foreign taxes; possible investment in securities of companies in
developing as well as developed countries; and sometimes less advantageous
legal, operational, and financial protections applicable to foreign subcustodial
arrangements. In addition, the costs of investing in foreign securities are
higher than the costs of investing in U.S. securities.

     Although the Funds try to invest in companies and governments of countries
having stable political environments, there is the possibility of expropriation
or confiscatory taxation, seizure, or nationalization of foreign bank deposits
or other assets, establishment of exchange controls, the adoption of foreign
government restrictions, or other adverse political, social, or diplomatic
developments that could affect investment in these nations.
    
Currency Exchange Transactions     

     The Funds may enter into currency exchange transactions. A currency
exchange transaction may be conducted either on a spot (i.e., cash) basis at the
spot rate for purchasing or selling currency prevailing in the foreign exchange
market or through a forward currency exchange contract ("forward contract"). A
forward contract is an agreement to purchase or sell a specified currency at a
specified future date (or within a specified time period) and price set at the
time of the contract. Forward contracts are usually entered into with banks,
foreign exchange dealers or broker-dealers, are not exchange-traded, and are
usually for less than one year, but may be renewed.

     Forward currency transactions may involve currencies of the different
countries in which a Fund may invest, and serve as hedges against possible
variations in the exchange rate between these currencies. The Funds' currency
transactions are limited to transaction hedging and portfolio hedging involving
either specific transactions or portfolio positions, except to the extent
described below under "Synthetic Foreign Money Market Positions." Transaction
hedging is the purchase or sale of a forward contract with respect to specific
payables or receivables of a Fund accruing in connection with the purchase or
sale of portfolio securities. Portfolio hedging is the use of a forward contract
with respect to a portfolio security position denominated or quoted in a
particular currency. Either Fund may engage in portfolio hedging with respect to
the currency of a particular country in amounts approximating actual or
anticipated positions in securities denominated in that currency. When a Fund
owns or anticipates owning securities in countries whose currencies are linked,
WAM may aggregate such positions as to the currency hedged.

     If a Fund enters into a forward contract hedging an anticipated purchase of
portfolio securities, assets of the Fund having a value at least as great as the
Fund's commitment under such forward contract will be segregated on the books of
the Fund and held by State Street Bank and Trust Company, the Funds' custodian
("State Street") while the contract is outstanding.

     At the maturity of a forward contract to deliver a particular currency, the
Fund may either sell the portfolio security related to such contract and make
delivery of the currency, or it may retain the security and either acquire the
currency on the spot market or terminate its contractual

                                       4
<PAGE>
 
obligation to deliver the currency by purchasing an offsetting contract with the
same currency trader obligating it to purchase on the same maturity date the
same amount of the currency.

     It is impossible to forecast with absolute precision the market value of
portfolio securities at the expiration of a forward contract. Accordingly, it
may be necessary for a Fund to purchase additional currency on the spot market
(and bear the expense of such purchase) if the market value of the security is
less than the amount of currency that the Fund is obligated to deliver and if a
decision is made to sell the security and make delivery of the currency.
Conversely, it may be necessary to sell on the spot market some of the currency
received upon the sale of the portfolio security if its market value exceeds the
amount of currency that fund is obligated to deliver.

     If a Fund retains the portfolio security and engages in an offsetting
transaction, the Fund will incur a gain or a loss to the extent that there has
been movement in forward contract prices. If a Fund engages in an offsetting
transaction, it may subsequently enter into a new forward contract to sell the
currency. Should forward prices decline during the period between a Fund's
entering into a forward contract for the sale of a currency and the date it
enters into an offsetting contract for the purchase of the currency, the Fund
will realize a gain to the extent the price of the currency it has agreed to
sell exceeds the price of the currency it has agreed to purchase. Should forward
prices increase, the Fund will suffer a loss to the extent the price of the
currency it has agreed to purchase exceeds the price of the currency it has
agreed to sell. A default on the contract would deprive the Fund of unrealized
profits or force the Fund to cover its commitments for purchase or sale of
currency, if any, at the current market price.

     Hedging against a decline in the value of a currency does not eliminate
fluctuations in the prices of portfolio securities or prevent losses if the
prices of such securities decline. Such transactions also preclude the
opportunity for gain if the value of the hedged currency should rise. Moreover,
it may not be possible for a Fund to hedge against a devaluation that is so
generally anticipated that the Fund is not able to contract to sell the currency
at a price above the devaluation level it anticipates. The cost to a Fund of
engaging in currency exchange transactions varies with such factors as the
currency involved, the length of the contract period, and prevailing market
conditions. Since currency exchange transactions are usually conducted on a
principal basis, no fees or commissions are involved.

     Synthetic Foreign Money Market Positions.  The Funds may invest in money
market instruments denominated in foreign currencies. In addition to, or in lieu
of, such direct investment, the Funds may construct a synthetic foreign money
market position by (a) purchasing a money market instrument denominated in one
currency (generally U.S. dollars) and (b) concurrently entering into a forward
contract to deliver a corresponding amount of that currency in exchange for a
different currency on a future date and at a specified rate of exchange. For
example, a synthetic money market position in Japanese yen could be constructed
by purchasing a U.S. dollar money market instrument and entering concurrently
into a forward contract to deliver a corresponding amount of U.S. dollars in
exchange for Japanese yen on a specified date and at a specified rate of
exchange. Because of the availability of a variety of highly liquid short-term
U.S. dollar money market instruments, a synthetic money market position
utilizing such U.S. dollar instruments may offer greater liquidity than direct
investment in foreign money market instruments. The results of a direct
investment in a foreign currency



                                       5
<PAGE>
 
and a concurrent construction of a synthetic position in such foreign currency,
in terms of both income yield and gain or loss from changes in currency exchange
rates, in general should be similar, but would not be identical, because the
components of the alternative investments would not be identical. Except to the
extent a synthetic foreign money market position consists of a money market
instrument denominated in a foreign currency, the synthetic foreign money market
position shall not be deemed a "foreign security" for purposes of the policies
that, under normal conditions, Acorn Twenty will not invest more than 15% of its
total assets in foreign securities and Acorn Foreign Forty will invest at least
85% of its total assets in foreign securities.

Options and Futures

     The Funds may purchase and write both call options and put options on
securities and on indexes, enter into interest rate and index futures contracts,
and may purchase or sell options on such futures contracts ("futures options")
in order to provide additional revenue, or to hedge against changes in security
prices or interest rates. The Funds may also use other types of options, futures
contracts and futures options currently traded or subsequently developed and
traded, provided the board of trustees determines that their use is consistent
with the Funds' investment objective.

     Options.  An option on a security (or index) is a contract that gives the
purchaser (holder) of the option, in return for a premium, the right to buy from
(call) or sell to (put) the seller (writer) of the option the security
underlying the option (or the cash value of the index) at a specified exercise
price at any time during the term of the option (normally not exceeding nine
months). The writer of an option on an individual security or on a foreign
currency has the obligation upon exercise of the option to deliver the
underlying security or foreign currency upon payment of the exercise price or to
pay the exercise price upon delivery of the underlying security or foreign
currency. Upon exercise, the writer of an option on an index is obligated to pay
the difference between the cash value of the index and the exercise price
multiplied by the specified multiplier for the index option. (An index is
designed to reflect specified facets of a particular financial or securities
market, a specific group of financial instruments or securities, or certain
economic indicators.)

     A Fund will write call options and put options only if they are "covered."
For example, in the case of a call option on a security, the option is "covered"
if the Fund owns the security underlying the call or has an absolute and
immediate right to acquire that security without additional consideration (or,
if additional consideration is required, assets having a value at least equal to
that amount are segregated on the books of the Fund) upon conversion or exchange
of other securities held in its portfolio.

     If an option written by a Fund expires, the Fund realizes a capital gain
equal to the premium received at the time the option was written. If an option
purchased by a Fund expires, the Fund realizes a capital loss equal to the
premium paid.

     Prior to the earlier of exercise or expiration, an option may be closed out
by an offsetting purchase or sale of an option of the same series (type,
exchange, underlying security or index,


                                       6
<PAGE>
 
exercise price and expiration). There can be no assurance, however, that a
closing purchase or sale transaction can be effected when a Fund desires.

     A Fund will realize a capital gain from a closing purchase transaction if
the cost of the closing option is less than the premium received from writing
the option, or, if it is more, the Fund will realize a capital loss.  If the
premium received from a closing sale transaction is more than the premium paid
to purchase the option, the Fund will realize a capital gain or, if it is less,
the Fund will realize a capital loss.  The principal factors affecting the
market value of a put or a call option include supply and demand, interest
rates, the current market price of the underlying security or index in relation
to the exercise price of the option, the volatility of the underlying security
or index, and the time remaining until the expiration date.

     A put or call option purchased by a Fund is an asset of that Fund and is
valued initially at the premium paid for the option.  The premium received for
an option written by the Fund is recorded as a deferred credit.  An option
purchased or written is "marked-to-market" daily and is valued at the closing
price on the exchange on which it is traded or, if not traded on an exchange or
no closing price is available, at the mean between the last bid and asked
prices.

     OTC Derivatives.  The Funds may buy and sell over-the-counter ("OTC")
derivatives (derivatives not traded on exchanges).  Unlike exchange-traded
derivatives, which are standardized with respect to the underlying instrument,
expiration date, contract size, and strike price, the terms of OTC derivatives
generally are established through negotiation with the other party to the
contract.  While this type of arrangement allows the Funds greater flexibility
to tailor an instrument to its needs, OTC derivatives generally involve greater
credit risk than exchange-traded derivatives, which are guaranteed by the
clearing organization of the exchanges where they are traded.  The Funds will
limit their investments so that no more than 5% of its total assets will be
placed at risk in the use of OTC derivatives.  See "Illiquid Securities" below
for more information on the risks associated with investing in OTC derivatives.

     Risks Associated with Options.  There are several risks associated with
transactions in options.  For example, there are significant differences between
the securities markets, the currency markets, and the options markets that could
result in an imperfect correlation between these markets, causing a given
transaction not to achieve its objectives.  A decision as to whether, when, and
how to use options involves the exercise of skill and judgment, and even a well-
conceived transaction may be unsuccessful to some degree because of market
behavior or unexpected events.
     
     There can be no assurance that a liquid market will exist when a Fund seeks
to close out an option position.  If a Fund were unable to close out an option
that it had purchased on a security, it would have to exercise the option in
order to realize any profit or the option would expire and become worthless.  If
a Fund were unable to close out a covered call option that it had written on a
security, it would not be able to sell the underlying security until the option
expired.  As the writer of a covered call option on a security, a Fund foregoes,
during the option's life, the opportunity to profit from increases in the market
value of the security covering the call option above the sum of the premium and
the exercise price of the call.  As the writer of a covered call option on a
foreign currency, a Fund foregoes, during the option's life, the opportunity to
profit from currency appreciation.

                                       7
<PAGE>
    
     If trading were suspended in an option purchased or written by a Fund, it
would not be able to close out the option.  If restrictions on exercise were
imposed, the Fund might be unable to exercise an option it has purchased.

     Futures Contracts and Options on Futures Contracts.  The Funds may use
interest rate futures contracts and index futures contracts.  An interest rate
or index futures contract provides for the future sale by one party and purchase
by another party of a specified quantity of a financial instrument or the cash
value of an index/1/ at a specified price and time.  A public market exists in
futures contracts covering a number of indexes (including, but not limited to:
the Standard & Poor's 500 Index; the Value Line Composite Index; the Russell
2000 Index; and the New York Stock Exchange Composite Index) as well as
financial instruments (including, but not limited to: U.S. Treasury bonds; U.S.
Treasury notes; Eurodollar certificates of deposit; and foreign currencies).
Other index and financial instrument futures contracts are available and it is
expected that additional futures contracts will be developed and traded.


     The Funds may purchase and write call and put options on futures.  Options
on futures possess many of the same characteristics as options on securities and
indexes (discussed above).  A futures option gives the holder the right, in
return for the premium paid, to assume a long position (call) or short position
(put) in a futures contract at a specified exercise price at any time during the
period of the option.  Upon exercise of a call option, the holder acquires a
long position in the futures contract and the writer is assigned the opposite
short position.  In the case of a put option, the opposite is true.

     To the extent required by regulatory authorities having jurisdiction over
the Funds, the Fund will limit their use of futures contracts and futures
options to hedging transactions.  For example, a Fund might use futures
contracts to hedge against fluctuations in the general level of stock prices,
anticipated changes in interest rates, or currency fluctuations that might
adversely affect either the value of its securities or the price of the
securities that the Fund intends to purchase.  A Fund's hedging may include
sales of futures contracts as an offset against the effect of expected declines
in stock prices or currency exchange rates or increases in interest rates and
purchases of futures contracts as an offset against the effect of expected
increases in stock prices or currency exchange rates or declines in interest
rates.  Although other techniques could be used to reduce the Fund's exposure to
stock price, interest rate, and currency fluctuations, a Fund may be able to
hedge its exposure more effectively and perhaps at a lower cost by using futures
contracts and futures options.

     The success of any hedging technique depends on WAM's ability to correctly
predict changes in the level and direction of stock prices, interest rates,
currency exchange rates, and other factors.  Should those predictions be
incorrect, the Fund's return might have been better had hedging not been
attempted; however, in the absence of the ability to hedge, WAM might 

/1/A futures contract on an index is an agreement pursuant to which two parties
agree to take or make delivery of an amount of cash equal to the difference
between the value of the index at the close of the last trading day of the
contract and the price at which the index contract was originally written.
Although the value of a securities index is a function of the value of certain
specified securities, no physical delivery of those securities is made.

                                       8
<PAGE>
 
have taken portfolio actions in anticipation of the same market movements with
similar investment results but, presumably, at greater transaction costs.

     When a purchase or sale of a futures contract is made by a Fund, it is
required to deposit with State Street or its broker a specified amount of cash
or U.S. government securities or other securities acceptable to the broker
("initial margin").  The margin required for a futures contract is generally set
by the exchange on which the contract is traded; however, the margin requirement
may be modified during the term of the contract, and the Fund's broker may
require margin deposits in excess of the minimum required by the exchange.  The
initial margin is in the nature of a performance bond or good faith deposit on
the futures contract, which is returned to the Fund upon termination of the
contract, assuming all contractual obligations have been satisfied.  The Funds
expect to earn interest income on their initial margin deposits.  A futures
contract held by a Fund is valued daily at the official settlement price of the
exchange on which it is traded.  Each day the Fund pays or receives cash, called
"variation margin," equal to the daily change in value of the futures contract.
This process is known as "marking-to-market."  Variation margin paid or received
by a Fund does not represent a borrowing or loan by the Fund but is instead
settlement between the Fund and the broker of the amount one would owe the other
if the futures contract had been offset at the close of the previous day.  In
computing daily NAV, the Funds will mark-to-market their open futures positions.
    
     The Funds are also required to deposit and maintain margin with respect to
put and call options on futures contracts they write.  Such margin deposits will
vary depending on the nature of the underlying futures contract (and the related
initial margin requirements), the current market value of the option, and other
futures positions held by the Funds.

     Although some futures contracts require making or taking delivery of the
underlying securities, usually these obligations are closed out prior to
delivery by offsetting purchases or sales of matching futures contracts (same
exchange, underlying security or index, and delivery month).  If an offsetting
purchase price is less than the original sale price, the Fund realizes a capital
gain, or if it is more, the Fund realizes a capital loss.  Conversely, if an
offsetting sale price is more than the original purchase price, the Fund
realizes a capital gain, or if it is less, the Fund realizes a capital loss.
The transaction costs must also be included in these calculations.
   
     Risks Associated with Futures.  There are several risks associated with the
use of futures contracts and futures options as hedging techniques.  A purchase
or sale of a futures contract may result in losses in excess of the amount
invested in the futures contract.  There can be no guarantee that there will be
a correlation between price movements in the hedging vehicle and in the
portfolio securities being hedged.  In addition, there are significant
differences between the securities and futures markets that could result in an
imperfect correlation between the markets, causing a given hedge not to achieve
its objectives.  The degree of imperfection of correlation depends on
circumstances such as: variations in speculative market demand for futures,
futures options, and the related securities, including technical influences in
futures and futures options trading and differences between the Funds'
investments being hedged and the securities underlying the standard contracts
available for trading.  For example, in the case of index futures contracts, the
composition of the index, including the issues and the weighting of each issue,
may differ from the composition of a Fund's portfolio, and, in the case of
interest rate futures contracts, the interest rate levels, maturities, and
creditworthiness of the issues underlying 
   
                                       9
<PAGE>
 
the futures contract may differ from the financial instruments held in a Fund's
portfolio. A decision as to whether, when, and how to hedge involves the
exercise of skill and judgment, and even a well-conceived hedge may be
unsuccessful to some degree because of market behavior or unexpected stock price
or interest rate trends.

     Futures exchanges may limit the amount of fluctuation permitted in certain
futures contract prices during a single trading day.  The daily limit
establishes the maximum amount that the price of a futures contract may vary
either up or down from the previous day's settlement price at the end of the
current trading session.  Once the daily limit has been reached in a futures
contract subject to the limit, no more trades may be made on that day at a price
beyond that limit.  The daily limit governs only price movements during a
particular trading day and therefore does not limit potential losses because the
limit may work to prevent the liquidation of unfavorable positions.  For
example, futures prices have occasionally moved to the daily limit for several
consecutive trading days with little or no trading, thereby preventing prompt
liquidation of positions and subjecting some holders of futures contracts to
substantial losses.  Stock index futures contracts are not normally subject to
such daily price change limitations.

     There can be no assurance that a liquid market will exist at a time when a
Fund seeks to close out a futures or futures option position.  The Fund would be
exposed to possible loss on the position during the interval of inability to
close, and would continue to be required to meet margin requirements until the
position is closed.  In addition, many of the contracts discussed above are
relatively new instruments without a significant trading history.  As a result,
there can be no assurance that an active secondary (liquid) market will develop
or continue to exist.

     Limitations on Options and Futures.  A Fund will not enter into a futures
contract or purchase an option thereon if, immediately thereafter, the initial
margin deposits for futures contracts held by the Fund plus premiums paid by it
for open futures option positions, less the amount by which any such positions
are "in-the-money,"/2/  would exceed 5% of the Fund's total assets.

     When purchasing a futures contract or writing a put option on a futures
contract, a Fund must maintain with State Street or its broker readily-
marketable securities having a fair market value (including any margin) at least
equal to the market value of such contract.  When writing a call option on a
futures contract, the Fund similarly will maintain with State Street readily-
marketable securities having a fair market value (including any margin) at least
equal to the amount by which such option is in-the-money until the option
expires or is closed out by the Fund.
___________________________
/2/A call option is "in-the-money" if the value of the futures contract that is
the subject of the option exceeds the exercise price.  A put option is "in-the-
money" if the exercise price exceeds the value of the futures contract that is
the subject of the option.

                                       10
<PAGE>
 
     A Fund may not maintain open short positions in futures contracts, call
options written on futures contracts, or call options written on indexes if, in
the aggregate, the market value of all such open positions exceeds the current
value of the securities in its portfolio, plus or minus unrealized gains and
losses on the open positions, adjusted for the historical relative volatility of
the relationship between the portfolio and the positions.  For this purpose, to
the extent a Fund has written call options on specific securities in its
portfolio, the value of those securities will be deducted from the current
market value of the securities portfolio.
  
     In order to comply with Commodity Futures Trading Commission Regulation 4.5
and thereby avoid being deemed a "commodity pool operator," the "underlying
commodity value" of each long position in a commodity contract in which the
Funds invest will not at any time exceed the sum of:

     (1)  The value of short-term U.S. debt obligations or other U.S. dollar
          denominated high-quality short-term money market instruments and cash
          set aside in an identifiable manner, plus any funds deposited as
          margin on the contract;

     (2)  Unrealized appreciation on the contract held by the broker; and

     (3)  Cash proceeds from existing investments due in not more than 30 days.

     "Underlying commodity value" means the size of the contract multiplied by
the daily settlement price of the contract.

     Neither Fund will purchase puts, calls, straddles, spreads, or any
combination thereof if by reason of such purchase more than 10% of its total
assets would be invested in such securities.

     Taxation of Options and Futures.    If a Fund exercises a call or put
option that it holds, the premium paid for the option is added to the cost basis
of the security purchased (call) or deducted from the proceeds of the security
sold (put).  For cash settlement options and futures options exercised by the
Fund, the difference between the cash received at exercise and the premium paid
is a capital gain or loss.

     If a call or put option written by a Fund is exercised, the premium is
included in the proceeds of the sale of the underlying security (call) or
reduces the cost basis of the security purchased (put).  For cash settlement
options and futures options written by a Fund, the difference between the cash
paid at exercise and the premium received is a capital gain or loss.

     Entry into a closing purchase transaction will result in capital gain or
loss.  If an option written by a Fund is in-the-money at the time it was written
and the security covering the option was held for more than the long-term
holding period prior to the writing of the option, any loss realized as a result
of a closing purchase transaction will be long-term.  The holding period of the
securities covering an in-the-money option will not include the period of time
the option is outstanding.
     
                                       11
<PAGE>
 
     If a Fund writes an equity call option/3/ other than a "qualified covered
call option," as defined in the Internal Revenue Code, any loss on such option
transaction, to the extent it does not exceed the unrealized gains on the
securities covering the option, may be subject to deferral until the securities
covering the option have been sold.

     A futures contract held until delivery results in capital gain or loss
equal to the difference between the price at which the futures contract was
entered into and the settlement price on the earlier of delivery notice date or
expiration date.  If a Fund delivers securities under a futures contract, the
Fund also realizes a capital gain or loss on those securities.

     For federal income tax purposes, the Funds generally are required to
recognize for each taxable year their net unrealized gains and losses as of the
end of the year on futures, futures options, and non-equity options positions
("year-end mark-to-market").  Generally, any gain or loss recognized with
respect to such positions (either by year-end mark-to-market or by actual
closing of the positions) is considered to be 60% long-term and 40% short-term,
without regard to the holding periods of the contracts.  However, in the case of
positions classified as part of a "mixed straddle," the recognition of losses on
certain positions (including options, futures and futures options positions, the
related securities and certain successor positions thereto) may be deferred to a
later taxable year.  Sale of futures contracts or writing of call options (or
futures call options) or buying put options (or futures put options) that are
intended to hedge against a change in the value of securities held by a fund may
affect the holding period of the hedged securities.

     If a Fund were to enter into a short index future, short index futures
option, or short index option position and the Fund's portfolio were deemed to
"mimic" the performance of the index underlying such contract, the option or
futures contract position and the Fund's stock positions may be deemed to be
positions in a mixed straddle, subject to the above-mentioned loss deferral
rules.

     The Taxpayer Relief Act of 1997 (the "Act") imposed constructive sale
treatment for federal income tax purposes on certain hedging strategies with
respect to appreciated securities.  Under these rules taxpayers will recognize
gain, but not loss, with respect to securities if they enter into short sales of
"offsetting notional principal contracts" (as defined by the Act) with respect
to, or futures or "forward contracts" (as defined by the Act) with respect to,
the same or substantially identical property, or if they enter into such
transactions and then acquire the same or substantially identical property.  The
Secretary of the Treasury is authorized to promulgate regulations that will
treat as constructive sales certain transactions that have substantially the
same effect as short sales, offsetting notional principal contracts, and futures
or forward contracts to deliver the same or substantially similar property.
___________________________
/3/An equity option is defined to mean any option to buy or sell stock, and any
other option the value of which is determined by reference to an index of stocks
of the type that is ineligible to be traded on a commodity futures exchange
(e.g., an option contract on a sub-index based on the price of nine hotel-casino
stocks).  The definition of equity option excludes options on broad-based stock
indexes (such as the Standard & Poor's 500 index).

                                       12
<PAGE>
 
     In order for each Fund to qualify for federal income tax treatment as a
regulated investment company, at least 90% of its gross income for a taxable
year must be derived from qualifying income, i.e., dividends, interest, income
derived from loans of securities, and gains from the sale of securities or
foreign currencies, or other income (including but not limited to gains from
options, futures, or forward contracts).  Any net gain realized from futures (or
futures options) contracts will be considered gain from the sale of securities
and therefore be qualifying income for purposes of the 90% requirement.
  
     Each Fund intends to distribute to shareholders annually any capital gains
that have been recognized for federal income tax purposes (including year-end
mark-to-market gains) on options and futures transactions, together with gains
on other Fund investments, to the extent such gains exceed recognized capital
losses and any net capital loss carryovers of the Fund.   Shareholders will be
advised of the nature of such capital gain distributions.

     For further information, see the discussion under "Additional Tax
Information."

     Swap Agreements.  A swap agreement is generally individually negotiated and
structured to include exposure to a variety of different types of investments or
market factors.  Depending on its structure, a swap agreement may increase or
decrease a Fund's exposure to changes in the value of an index of securities in
which the Fund might invest, the value of a particular security or group of
securities, or foreign currency values.  Swap agreements can take many different
forms and are known by a variety of names.  A Fund may enter into any form of
swap agreement if WAM determines it is consistent with its investment objective
and policies, but each Fund will limit its use of swap agreements so that no
more than 5% of its total assets will be invested in such agreements.

     A swap agreement tends to shift a Fund's investment exposure from one type
of investment to another.  For example, if a Fund agrees to exchange payments in
dollars at a fixed rate for payments in a foreign currency the amount of which
is determined by movements of a foreign securities index, the swap agreement
would tend to increase the Fund's exposure to foreign stock market movements and
foreign currencies.  Depending on how it is used, a swap agreement may increase
or decrease the overall volatility of a Fund's investments and its NAV.

     The performance of a swap agreement is determined by the change in the
specific currency, market index, security, or other factors that determine the
amounts of payments due to and from the Fund.  If a swap agreement calls for
payments by a Fund, the Fund must be prepared to make such payments when due.
If the counterparty's creditworthiness declines, the value of a swap agreement
would be likely to decline, potentially resulting in a loss.  WAM expects to be
able to eliminate each Fund's exposure under any swap agreement either by
assignment or by other disposition, or by entering into an offsetting swap
agreement with the same party or a similarly creditworthy party.
 
     Each Fund will segregate its assets to cover its current obligations under
a swap agreement.  If a Fund enters into a swap agreement on a net basis, it
will segregate assets with a daily value at least equal to the excess, if any,
of its accumulated obligations under the swap agreement over the accumulated
amount the Fund is entitled to receive under the agreement.  If a 

                                       13
<PAGE>
 
Fund enters into a swap agreement on other than a net basis, it will segregate
assets with a value equal to the full amount of its accumulated obligations
under the agreement.

     Short Sales Against the Box. Each Fund may make short sales of securities
if at all times, when a short position is open, the Fund owns an equal amount of
such securities or securities convertible into or exchangeable for, without
payment of any further consideration, securities of the same issue as, and equal
in amount to, the securities sold short. This technique is called selling short
"against the box." Although permitted by its investment restrictions, the Funds
do not currently intend to sell securities short.

     In a short sale against the box, a Fund does not deliver from its portfolio
the securities sold and does not receive immediately the proceeds from the short
sale. Instead, the Fund borrows the securities sold short from a broker-dealer
through which the short sale is executed, and the broker-dealer delivers such
securities, on behalf of the Fund, to the purchaser of such securities. Such
broker-dealer is entitled to retain the proceeds from the short sale until the
Fund delivers to such broker-dealer the securities sold short. In addition, the
Fund is required to pay to the broker-dealer the amount of any dividends paid on
shares sold short. Finally, to secure its obligation to deliver to such broker-
dealer the securities sold short, the Fund must deposit and continuously
maintain in a separate account with State Street an equivalent amount of the
securities sold short or securities convertible into or exchangeable for such
securities without the payment of additional consideration. The Fund is said to
have a short position in the securities sold until it delivers to the broker-
dealer the securities sold, at which time the Fund receives the proceeds of the
sale. Because the Fund ordinarily will want to continue to hold securities in
its portfolio that are sold short, the Fund will normally close out a short
position by purchasing on the open market and delivering to the broker-dealer an
equal amount of the securities sold short, rather than by delivering portfolio
securities.

     Short sales may protect a Fund against the risk of losses in the value of
its portfolio securities because any unrealized losses with respect to such
portfolio securities should be wholly or partially offset by a corresponding
gain in the short position. However, any potential gains in such portfolio
securities should be wholly or partially offset by a corresponding loss in the
short position. The extent to which such gains or losses are offset will depend
upon the amount of securities sold short relative to the amount the Fund owns,
either directly or indirectly, and, in the case where the Fund owns convertible
securities, changes in the conversion premium. The Funds will incur transaction
costs in connection with short sales.

     In addition to enabling the Funds to hedge against market risk, short sales
may afford a Fund an opportunity to earn additional current income to the extent
the Fund is able to enter into arrangements with broker-dealers through which
the short sales are executed to receive income with respect to the proceeds of
the short sales during the period the Fund's short positions remain open.

     The Taxpayer Relief Act of 1997 (see page 13) imposed constructive sale
treatment for federal income tax purposes on certain hedging strategies with
respect to appreciated securities. Under these rules taxpayers will recognize
gain, but not loss, with respect to securities if they enter into short sales of
"offsetting notional principal contracts" (as defined by the Act) with respect
to the same or substantially identical property, or if they enter into such
transactions and

                                      14
<PAGE>
 
then acquire the same or substantially identical property. The Secretary of the
Treasury is authorized to promulgate regulations that will treat as constructive
sales certain transactions that have substantially the same effect as short
sales.

Debt Securities

     Both Funds may invest in debt securities, including lower-rated securities
(i.e., securities rated BB or lower by Standard & Poor's Corporation ("S&P") or
Ba or lower by Moody's Investor Services, Inc. ("Moody's"), commonly called
"junk bonds"), and securities that are not rated. There are no restrictions as
to the ratings of debt securities acquired by either Fund or the portion of each
Fund's assets that may be invested in debt securities in a particular ratings
category. Neither Fund intends to invest more than 20% of its total assets in
debt securities nor more than 5% of its total assets in securities rated at or
lower than the lowest investment grade.

     Securities rated BBB or Baa are considered to be medium grade and to have
speculative characteristics. Lower-rated debt securities are predominantly
speculative with respect to the issuer's capacity to pay interest and repay
principal. Investment in medium- or lower-quality debt securities involves
greater investment risk, including the possibility of issuer default or
bankruptcy. An economic downturn could severely disrupt the market for such
securities and adversely affect the value of such securities. In addition, 
lower-quality bonds are less sensitive to interest rate changes than higher-
quality instruments and generally are more sensitive to adverse economic changes
or individual corporate developments. During a period of adverse economic
changes, including a period of rising interest rates, the junk bond market may
be severely disrupted, and issuers of such bonds may experience difficulty in
servicing their principal and interest payment obligations.

     Medium- and lower-quality debt securities may be less marketable than
higher quality debt securities because the market for them is less broad. The
market for unrated debt securities is even narrower. During periods of thin
trading in these markets, the spread between bid and asked prices is likely to
increase significantly, and a Fund may have greater difficulty selling its
portfolio securities. See "Purchasing and Redeeming Shares Net Asset Value." The
market value of these securities and their liquidity may be affected by adverse
publicity and investor perceptions. A more complete description of the
characteristics of bonds in each ratings category is included in the appendix to
this SAI.

Illiquid Securities

     Neither Fund may invest in illiquid securities, including restricted
securities and OTC derivatives, if as a result, they would comprise more than
15% of the value of its net assets.

     Restricted securities may be sold only in privately negotiated transactions
or in a public offering with respect to which a registration statement is in
effect under the Securities Act of 1933 (the "1933 Act"). Where registration is
required, a Fund may be obligated to pay all or part of the registration
expenses and a considerable period may elapse between the time of the decision
to sell and the time the Fund may be permitted to sell a security under an
effective registration statement. If, during such a period, adverse market
conditions were to develop, the Fund might obtain a less favorable price than
prevailed when it decided to sell. Restricted

                                      15
<PAGE>
 
securities will be priced at a fair value as determined in good faith by the
board of trustees. If, through the appreciation of illiquid securities or the
depreciation of liquid securities, either Fund should be in a position where
more than 15% of the value of its net assets are invested in illiquid assets,
including restricted securities and OTC derivatives, that Fund will take
appropriate steps to protect liquidity.

     Notwithstanding the above, either Fund may purchase securities that have
been privately placed but that are eligible for purchase and sale under Rule
144A under the 1933 Act. That rule permits certain qualified institutional
buyers, such as the Funds, to trade in privately placed securities that have not
been registered for sale under the 1933 Act. WAM, under the supervision of the
board of trustees, will consider whether securities purchased under Rule 144A
are illiquid and thus subject to each Fund's restriction of investing no more
than 15% of the value of its assets in illiquid securities. A determination of
whether a Rule 144A security is liquid or not is a question of fact. In making
this determination WAM will consider the trading markets for the specific
security taking into account the unregistered nature of a Rule 144A security. In
addition, WAM could consider the (1) frequency of trades and quotes, (2) number
of dealers and potential purchasers, (3) dealer undertakings to make a market,
and (4) nature of the security and of market place trades (e.g., the time needed
to dispose of the security, the method of soliciting offers, and the mechanics
of transfer). The liquidity of Rule 144A securities would be monitored and if,
as a result of changed conditions, it is determined that a Rule 144A security is
no longer liquid, a Fund's holdings of illiquid securities would be reviewed to
determine what, if any, steps are required to assure that it does not invest
more than 15% of its assets in illiquid securities. Investing in Rule 144A
securities could have the effect of increasing the amount of a Fund's assets
invested in illiquid securities if qualified institutional buyers are unwilling
to purchase such securities.

Repurchase Agreements

     Repurchase agreements are transactions in which a Fund purchases a security
from a bank or recognized securities dealer and simultaneously commits to resell
that security to the bank or dealer at an agreed-upon price, date, and market
rate of interest unrelated to the coupon rate or maturity of the purchased
security. Although repurchase agreements carry certain risks not associated with
direct investments in securities, the Funds will enter into repurchase
agreements only with banks and dealers WAM believes present minimum credit risks
in accordance with guidelines approved by the board of trustees. WAM will review
and monitor the creditworthiness of such institutions, and will consider the
capitalization of the institution, WAM's prior dealings with the institution,
any rating of the institution's senior long-term debt by independent rating
agencies, and other relevant factors.

     A Fund will invest only in repurchase agreements collateralized at all
times in an amount at least equal to the repurchase price plus accrued interest.
To the extent that the proceeds from any sale of such collateral upon a default
in the obligation to repurchase were less than the repurchase price, the Fund
would suffer a loss. If the financial institution which is party to the
repurchase agreement petitions for bankruptcy or otherwise becomes subject to
bankruptcy or other liquidation proceedings there may be restrictions on the
Fund's ability to sell the collateral and the Fund could suffer a loss. However,
with respect to financial institutions whose bankruptcy or liquidation
proceedings are subject to the U.S. Bankruptcy Code, each Fund
                                       
                                      16
<PAGE>
 
intends to comply with provisions under such Code that would allow it
immediately to resell such collateral. Under normal circumstances, neither Fund
intends to invest more than 5% of its total assets in repurchase agreements.
    
When-Issued and Delayed Delivery Securities; Reverse Repurchase Agreements     

     A Fund may purchase securities on a when-issued or delayed delivery basis.
Although the payment and interest terms of these securities are established at
the time a Fund enters into the commitment, the securities may be delivered and
paid for a month or more after the date of purchase, when their value may have
changed. A Fund makes such commitments only with the intention of actually
acquiring the securities, but may sell the securities before the settlement date
if WAM deems it advisable for investment reasons. A Fund may utilize spot and
forward foreign currency exchange transactions to reduce the risk inherent in
fluctuations in the exchange rate between one currency and another when
securities are purchased or sold on a when-issued or delayed delivery basis.

     A Fund may enter into reverse repurchase agreements with banks and
securities dealers. A reverse repurchase agreement is a repurchase agreement in
which the Fund is the seller of, rather than the investor in, securities and
agrees to repurchase them at an agreed-upon time and price. Use of a reverse
repurchase agreement may be preferable to a regular sale and later repurchase of
securities because it avoids certain market risks and transaction costs.

     At the time a Fund enters into a binding obligation to purchase securities
on a when-issued basis or enters into a reverse repurchase agreement, assets of
the Fund having a value at least as great as the purchase price of the
securities to be purchased will be segregated on the books of the Fund and held
by State Street throughout the period of the obligation. The use of these
investment strategies, as well as any borrowing by the Fund, may increase NAV
fluctuation. The Funds have no present intention of investing in reverse
repurchase agreements.

Temporary Strategies

     Both Funds have the flexibility to respond promptly to changes in market
and economic conditions. In the interest of preserving shareholders' capital,
WAM may employ a temporary defensive investment strategy if it determines such a
strategy to be warranted. Pursuant to such a defensive strategy, each Fund
temporarily may hold cash (U.S. dollars, foreign currencies, multinational
currency units) and/or invest up to 100% of its assets in high quality debt
securities or money market instruments of U.S. or foreign issuers, and most or
all of the Fund's investments may be made in the United States and denominated
in U.S. dollars. It is impossible to predict whether, when, or for how long a
Fund might employ defensive strategies.

     In addition, pending investment of proceeds from new sales of Fund shares
or to meet ordinary daily cash needs, a Fund temporarily may hold cash (U.S.
dollars, foreign currencies, or multinational currency units) and may invest any
portion of its assets in money market instruments.

                                      17
<PAGE>
 
Portfolio Turnover

     Although the Funds do not purchase securities with a view to rapid
turnover, there are no limitations on the length of time that portfolio
securities must be held. Portfolio turnover can occur for a number of reasons
such as general conditions in the securities markets, more favorable investment
opportunities in other securities, or other factors relating to the desirability
of holding or changing a portfolio investment. Each Fund's portfolio turnover
rate is not expected to exceed 50% under normal market conditions. A high rate
of portfolio turnover, if it should occur, would result in increased transaction
expenses which must be borne by the Funds. High portfolio turnover may also
result in the realization of capital gains or losses and, to the extent net
short-term capital gains are realized, any distributions resulting from such
gains will be considered ordinary income for federal income tax purposes.

Line of Credit

     Acorn maintains a line of credit with a bank in order to permit borrowing
on a temporary basis to meet share redemption requests in circumstances in which
temporary borrowing may be preferable to liquidation of portfolio securities.
Any borrowings under that line of credit by the Funds would be subject to the
Funds' restrictions on borrowing under "Investment Restrictions," below.

Investment Restrictions

     In pursuing their investment objectives, neither Fund will:

     1.  Acquire securities of any one issuer, which at the time of investment
     (a) represent more than 10% of the voting securities of the issuer or (b)
     have a value greater than 10% of the value of the outstanding securities of
     the issuer;

     2.  With respect to 50% of its total assets, purchase the securities of any
     issuer (other than cash items and U.S. government securities and securities
     of other investment companies) if such purchase would cause the Fund's
     holdings of that issuer to exceed more than 5% of the Fund's total assets;

     3.  Invest more than 25% of its total assets in a single issuer (other than
     U.S. government securities);

     4.  Invest more than 25% of its total assets in the securities of companies
     in a single industry (excluding U.S. government securities);

     5.  Make loans, but this restriction shall not prevent the Fund from (a)
     investing in debt securities, (b) investing in repurchase agreements, or
     (c) lending its portfolio securities, provided that it may not lend
     securities if, as a result, the aggregate value of all securities loaned
     would exceed 33% of its total assets (taken at market value at the time of
     such loan);

     6.  Borrow money except (a) from banks for temporary or emergency purposes
     in amounts not exceeding 33% of the value of the Fund's total assets at 

                                      18
<PAGE>
 
     the time of borrowing, and (b) in connection with transactions in options,
     futures, and options on futures;

     7.   Underwrite the distribution of securities of other issuers; however,
     the Fund may acquire "restricted" securities which, in the event of a
     resale, might be required to be registered under the Securities Act of 1933
     on the ground that the Fund could be regarded as an underwriter as defined
     by that act with respect to such resale;

     8.   Purchase and sell real estate or interests in real estate, although it
     may invest in marketable securities of enterprises which invest in real
     estate or interests in real estate;

     9.   Purchase and sell commodities or commodity contracts, except that it
     may enter into (a) futures and options on futures and (b) foreign currency
     contracts;

     10.  Make margin purchases of securities, except for use of such short-term
     credits as are needed for clearance of transactions and except in
     connection with transactions in options, futures, and options on futures;

     11.  Issue any senior security except to the extent permitted under the
     Investment Company Act of 1940.

     The above restrictions for each Fund are "fundamental," which means that
they cannot be changed without the approval of the lesser of (i) 67% of each
fund's shares present at a meeting if more than 50% of the shares outstanding
are present or (ii) more than 50% of each fund's outstanding shares.

     In addition, the Funds are subject to a number of restrictions that may be
changed by the board of trustees without shareholder approval.  Under those non-
fundamental restrictions, neither Fund will:

     (a) Invest in companies for the purpose of management or the exercise of
     control;

     (b) Acquire securities of other registered investment companies except in
     compliance with the Investment Company Act of 1940;

     (c) Invest more than 15% of its net assets (valued at time of investment)
     in illiquid securities, including repurchase agreements maturing in more
     than seven days;

     (d) Pledge, mortgage or hypothecate its assets, except as may be necessary
     in connection with permitted borrowings or in connection with short sales,
     options, futures, and options on futures;

     (e) Make short sales of securities unless the Fund owns at least an equal
     amount of such securities, or owns securities that are convertible or
     exchangeable, 

                                       19
<PAGE>
 
     without payment of further consideration, into at least an equal amount of
     such securities;

     (f) [Acorn Twenty only] Invest more than 15% of its total assets in the
     securities of foreign issuers.

     (g) [Acorn Foreign Forty only] Invest more than 15% of its total assets in
     securities of United States issuers, under normal market conditions.

     Notwithstanding the foregoing investment restrictions, the Funds may
purchase securities pursuant to the exercise of subscription rights.

                            Performance Information

     From time to time the Funds may quote total return figures. "Total Return"
for a period is the percentage change in value during the period of an
investment in shares of the Fund, including the value of shares acquired through
reinvestment of all dividends and capital gains distributions.  "Average Annual
Total Return" is the average annual compounded rate of change in value
represented by the Total Return for the period.

     Average Annual Total Return is computed as follows:

          ERV = P(1+T)/n/

     Where:  P = the amount of an assumed initial investment in shares of a fund
             T = average annual total return
             n = number of years from initial investment to the end of the 
                 period
             ERV = ending redeemable value of shares held at the end of the
                   period


     The Funds impose no sales charges and pay no distribution expenses.  Income
taxes are not taken into account.  Performance figures quoted by the Funds are
not necessarily indicative of future results.  The Funds' performance is a
function of conditions in the securities markets, portfolio management, and
operating expenses.  Although information about past performance is useful in
reviewing the Funds' performance and in providing some basis for comparison with
other investment alternatives, it should not be used for comparison with other
investments using different reinvestment assumptions or time periods.

     In advertising and sales literature, the Funds' performance may be compared
with those of market indexes and other mutual funds.  In addition to the
performance information described above, the Fund might use comparative
performance as computed in a ranking or rating determined by Lipper Analytical
Services, Inc., an independent service that monitors the performance of over
1,000 mutual funds, Morningstar, Inc., or another service.

     The Funds may note their mention or recognition in newsletters, newspapers,
magazines, or other media.  The Funds may similarly note mention or recognition
of WAM, or appearances of principals of WAM, in the media.

                                       20
<PAGE>
 
                               Investment Adviser

     Wanger Asset Management, L.P. ("WAM"), serves as the investment adviser for
the Funds, the other Acorn funds, and institutional accounts.  As of the date
of this SAI, WAM has approximately $7 billion under management, including the
Funds.  WAM is a limited partnership managed by its general partner, Wanger
Asset Management, Ltd. ("WAM Ltd."), whose stockholders are Ralph Wanger,
Charles P. McQuaid, Leah J. Zell, Marcel P. Houtzager, Robert A. Mohn, and John
H. Park.  Ralph Wanger is the president and Howard L. Kastel is the chief
executive officer of WAM Ltd.  On matters submitted to the shareholders of WAM
Ltd., each shareholder has one vote (or a lesser vote in the case of new
shareholders).  With certain exceptions (including for extraordinary
transactions, for which Mr. Wanger's consent is required), decisions are made by
majority vote.  WAM commenced operations in 1992.

     WAM furnishes continuing investment supervision to the Funds under an
investment advisory agreement (the "Agreement") and is responsible for overall
management of the Funds' business affairs.  It furnishes office space, equipment
and personnel to the Funds and assumes the expenses of printing and distributing
the Funds' prospectus and reports to prospective investors.  The Agreement will
continue in effect as to each of the Funds through June 30, 1999, and thereafter
from year to year so long as its continuance is approved at least annually by
(i) the board of trustees of Acorn Investment Trust or by the holders of a
majority of each Fund's outstanding voting securities as defined by the
Investment Company Act of 1940 and (ii) a majority of the members of Acorn's
board of trustees who are not otherwise affiliated with Acorn or WAM, cast in
person at a meeting called for that purpose.  Any amendment to the Agreement
must be approved in the same manner.  The Agreement may be terminated as to
either Fund without penalty by the vote of the board of trustees of Acorn or the
shareholders of that Fund (by a majority as defined in the 1940 Act) on 60 days'
written notice to WAM or by WAM on 60 days' notice to the Fund, and will
terminate automatically in the event of its assignment.

     The advisory fees the Funds pay to WAM are calculated daily and paid
monthly, at the following annual rates: Acorn Twenty, 0.90% of average net
assets; Acorn Foreign Forty, 0.95% of average net assets.

     Acorn has a separate administrative services agreement with WAM under which
WAM provides various administrative and clerical services such as the
maintenance of books and records, the calculation and publication of each Fund's
net asset value, and the calculation of dividends, distributions and performance
data for each Fund. WAM also furnishes corporate secretarial services to Acorn
and provides Acorn with administrative offices and data processing facilities.
Under the administrative services agreement, WAM receives a fee, calculated
daily and paid monthly, at the annual rate of 0.05 of 1% of the Funds' average
daily net assets.

     The Funds pay the cost of custodial, stock transfer, dividend disbursing,
audit and legal services, and membership in trade organizations.  They also pay
other expenses such as the cost of maintaining the registration of their shares
under federal law, complying with state securities laws, proxy solicitations,
printing and distributing notices and copies of the prospectus and shareholder
reports furnished to existing shareholders, taxes, insurance premiums, and the
fees of trustees not affiliated with WAM.

                                       21
<PAGE>
 
                                  Distributor

     Shares of the Funds are offered for sale by WAM Brokerage Services, L.L.C.
("WAM BD") without any sales commissions, 12b-1 fees, or other charges to the
Funds or their shareholders.  WAM BD is wholly-owned by WAM and WAM Ltd.  All
distribution expenses relating to the Funds are paid by WAM, including the
payment or reimbursement of any expenses incurred by WAM BD.  The Distribution
Agreement will continue in effect through June 30, 1999 and thereafter from year
to year provided such continuance is approved annually (i) by a majority of the
trustees or by a majority of the outstanding voting securities of the Trust, and
(ii) by a majority of the trustees who are not parties to the Agreement or
interested persons of any such party.

     The Trust has agreed to pay all expenses in connection with registration of
its shares with the Securities and Exchange Commission and any auditing and
filing fees required in compliance with various state securities laws.  WAM
bears all sales and promotional expenses, including the cost of prospectuses and
other materials used for sales and promotional purposes by WAM BD. WAM BD offers
the Funds' shares only on a best efforts basis.  WAM BD is located at 227 West
Monroe Street, Suite 3000, Chicago, Illinois 60606.

                                   The Trust

     The Trust is a Massachusetts business trust organized under an Agreement
and Declaration of Trust dated April 21, 1992 (the "Declaration of Trust").  The
Declaration of Trust may be amended by a vote of either the Trust's shareholders
or its trustees.  The Trust may issue an unlimited number of shares, in one or
more series as the board of trustees may authorize.  Any such series of shares
may be further divided, without shareholder approval, into two or more classes
of shares having such preferences or special or relative rights or privileges as
the trustees may determine.  The shares of the Acorn funds are not currently
divided into classes.  The board of trustees may authorize the issuance of
additional series of the Trust if deemed advisable, each with its own investment
objective, policies, and restrictions.  All shares issued will be fully paid and
non-assessable and will have no preemptive or conversion rights.

     Under Massachusetts law, the shareholders of the Trust may, under certain
circumstances believed to be remote, be held personally liable for the Trust's
obligations.  However, the Declaration of Trust disclaims liability of
shareholders and the Trust's trustees and officers for acts or obligations of
the Trust and requires that notice of such disclaimer be given in each
agreement, obligation, or contract entered into or executed by the Trust or the
board of trustees.  The Declaration of Trust provides for indemnification out of
the assets of the Trust of all losses and expenses of any shareholder held
personally liable for the obligations of the Trust.  Thus, the risk of a
shareholder incurring financial loss on account of shareholder liability is
remote, since it is limited to circumstances in which the disclaimer is
inoperative and the Trust itself is unable to meet its obligations.

     On any matter submitted to a vote of shareholders, shares are voted in the
aggregate and not by individual series except that shares are voted by
individual series when required by the Investment Company Act of 1940 or other
applicable law, or when the board of trustees determines that the matter affects
only the interests of one series, in which case shareholders of 

                                       22
<PAGE>
 
the unaffected series are not entitled to vote on such matters. All shares of
the Trust are voted together in the election of trustees.

                             Trustees and Officers

     The trustees and officers of the Trust, their dates of birth and their
principal business activities during the past five years are:

Irving B. Harris, trustee and chairman
     Two North LaSalle Street, Chicago, Illinois 60602; date of birth 8/4/1910;
     chairman of the executive committee and director, Pittway Corporation
     (multi-product manufacturer and publisher); chairman, William Harris
     Investors, Inc. (investment adviser); chairman, The Harris Foundation
     (charitable foundation); director, Teva Pharmaceutical Industries, Inc.
     (pharmaceutical manufacturer).

Ralph Wanger, trustee and president*
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     6/21/1934; trustee and president, Wanger Advisors Trust; principal, Wanger
     Asset Management, L.P.

James H. Lorie, trustee and vice chairman
     1101 East 58th Street, Chicago, Illinois 60637; date of birth 2/23/1922;
     retired; Eli B. and Harriet B. Williams Professor of Business
     Administration Emeritus, University of Chicago Graduate School of Business;
     director, Thornburg Mortgage Asset Corp. (REIT) and Santa Fe Natural
     Tobacco.

Leo A. Guthart, trustee
     165 Eileen Way, Syosset, New York 11791; date of birth 9/26/1937; vice
     chairman, Pittway Corporation (multi-product manufacturer and publisher);
     chief executive officer, Pittway Corporation's Security Group of Companies
     which include ADEMCO (manufacturer of alarm equipment), ADI (distributor of
     security equipment), Fire Burglary Instruments (supplier of security
     control panels), First Alert Professional (alarm dealers), Alarm Net
     (cellular radio service) and Cylink Corporation (supplier of encryption
     equipment)(chairman); director, AptarGroup, Inc. (producer of dispensing
     valves, pumps and closures); chairman of the board of trustees, Hofstra
     University; chairman, Tech Transfer Island Corp. (private investment
     partnership).

Jerome Kahn, Jr., trustee
     Two North LaSalle Street, Suite 400, Chicago, Illinois 60602; date of birth
     4/13/1934; vice president, William Harris Investors, Inc. (investment
     adviser); director, Pittway Corporation (multi-product manufacturer and
     publisher).

David C. Kleinman, trustee
     1101 East 58th Street, Chicago, Illinois 60637; date of birth 10/12/1935;
     senior lecturer in business administration, University of Chicago Graduate
     School of Business; business consultant; director, Irex Corporation
     (insulation contractor).

Charles P. McQuaid, trustee and senior vice president*
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     8/27/1953; trustee and senior vice president, Wanger Advisors Trust;
     principal and director of research, Wanger Asset Management, L.P.

                                       23
<PAGE>
 
Roger S. Meier, trustee
     1211 S. W. Fifth Avenue, Portland, Oregon 97204; date of birth 1/18/1926;
     president, AMCO, Inc. (investment and real estate management); director,
     Fred Meyer, Inc. (retail chain); director and advisory board member, Key
     Bank of Oregon (banking); chairman of Investment Council and member of
     Committee of Legacy Systems (hospital); executive director and chairman of
     investment committee, Portland Art Museum.

Adolph Meyer, Jr., trustee
     1511 West Webster Avenue, Chicago, Illinois 60614; date of birth
     11/26/1923; president, Gulco Corp. (leather manufacturer).
    
Marcel P. Houtzager, vice president
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     10/26/1960; vice president, Wanger Advisors Trust; principal, analyst, and
     portfolio manager, Wanger Asset Management, L.P.

Kenneth A. Kalina, assistant treasurer
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60603; date of birth
     8/4/1959; assistant treasurer, Wanger Advisors Trust; Fund controller,
     Wanger Asset Management, L.P., since September 1995; prior thereto,
     treasurer of the Stein Roe Mutual Funds.

Merrillyn J. Kosier, senior vice president and secretary
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     12/10/1959; vice president and secretary, Wanger Advisors Trust; director
     of marketing and shareholder services, Wanger Asset Management, L.P., since
     September 1993; prior thereto, vice president of marketing, Kemper
     Financial Services, Inc.

Bruce H. Lauer, vice president and treasurer
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     7/22/1957; vice president and treasurer, Wanger Advisors Trust; chief
     administrative officer, Wanger Asset Management, L.P. since April 1995;
     prior thereto, first vice president, investment accounting, Kemper
     Financial Services, Inc.

Robert A. Mohn, vice president
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     9/13/1961; vice president, Wanger Advisors Trust; principal, analyst and
     portfolio manager, Wanger Asset Management, L.P.

John H. Park, vice president
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     5/30/1967; vice president, Wanger Advisors Trust; principal (since 1998),
     analyst and portfolio manager, Wanger Asset Management, L.P. (since July
     1993).     
    
Mark H. Yost, vice president
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     6/28/1963; analyst and portfolio manager, Wanger Asset Management, L.P.,
     since October 1995; co-portfolio manager of Wanger U.S. Smaller Companies
     Fund since June 1997; portfolio manager of WAM Yost Partnership, L.P.;
     prior thereto, investment analyst, First Chicago Corporation.     
      
Leah J. Zell, vice president
     227 West Monroe Street, Suite 3000, Chicago, Illinois 60606; date of birth
     5/23/1949; vice president, Wanger Advisors Trust; principal, analyst and
     portfolio manager, Wanger Asset Management, L.P.      

     *Messrs. McQuaid and Wanger are trustees who are interested persons of
Acorn as defined in the Investment Company Act of 1940, and of WAM.  Messrs.
Harris, Lorie, and 

                                       24
<PAGE>
 
Wanger are members, and Mr. McQuaid is an alternate member, of the executive
committee, which has authority during intervals between meetings of the board of
trustees to exercise the powers of the board, with certain exceptions. As of May
1, 1998, the trustees and officers of Acorn as a group owned beneficially less
than 1% of the outstanding shares of the funds.

     The following table sets forth the total compensation paid by the Trust
during the fiscal year ended December 31, 1997 to each of the trustees of the
Trust:

<TABLE>
<CAPTION>
                     Aggregate       Aggregate     Aggregate         Total
                    Compensation   Compensation   Compensation    Compensation
Name of Trustee      from Acorn     from Acorn     from Acorn        from
                       Fund        International      USA        Fund Complex(3)
- --------------------------------------------------------------------------------
<S>                 <C>            <C>            <C>            <C>
Irving B. Harris      $53,900        $33,340         $1,760         $89,000
                                   
Leo A. Guthart         21,665         13,605            730          36,000
                                   
Jerome Kahn, Jr.       24,085         14,625            790          39,500
                                   
David C. Kleinman      24,085         14,625            790          39,500
                                   
James H. Lorie         18,775         11,100            625          30,500
                                   
Charles P. McQuaid          0              0              0               0
                                   
Roger S. Meier         21,665         13,105            730          35,500
                                   
Adolph Meyer, Jr.      19,600         11,740            660          32,000
                                   
Ralph Wanger                0              0              0               0
- ---------------------------------------------------------------------------
</TABLE>

     The officers and trustees affiliated with WAM serve without any
compensation from the Trust.  Acorn has adopted a deferred compensation plan
(the "Plan") which permits the trustees who are not "interested persons" of
Acorn or WAM ("participating trustees") to defer receipt of all or a portion of
their compensation from the Trust. Under the Plan, participating trustees may
defer receipt of all or a portion of their compensation in order to defer
payment of income taxes or for other reasons.  The deferred compensation payable
to a participating trustee is credited to a book reserve account as of the
business day such compensation would have been paid to such trustee. The
deferred compensation accrues income from the date of credit in an amount equal
to the amount that would have been earned had such deferred compensation (and
all income earned thereon) been invested and reinvested in shares of one or more
of the Funds.  If a participating trustee retires, such trustee may elect to
receive payments under the plan in a lump sum or in equal annual installments
over a period of five years.  If a participating trustee dies, any amount
payable under the Plan will be paid to that trustee's beneficiaries.  Each
Fund's obligation to make payments under the Plan is a general obligation of
that fund.  No other Fund will be liable for any other Fund's obligations to
make payments under the Plan.

                                       25
<PAGE>
 
                        Purchasing and Redeeming Shares

     Purchases and redemptions are discussed in the Funds' prospectus under the
headings "Your Account  How to Buy Shares" and "Your Account  How to Sell
Shares."  All of that information is incorporated herein by reference.

     Acorn may authorize from time to time certain financial services companies,
broker-dealers or their designees ("authorized agents") to accept share purchase
and redemption orders on behalf of the Funds.  Some of those authorized agents
may charge transaction fees for their services.  For purchase orders placed
through an authorized agent, a shareholder will pay the Fund's net asset value
("NAV") per share (see "Net Asset Value," below) next computed after the receipt
by the authorized agent of such purchase order, plus any applicable transaction
charge imposed by the agent.  For redemption orders placed through an authorized
agent, a shareholder will receive redemption proceeds which reflect the NAV per
share next computed after the receipt by the authorized agent of the redemption
order, less any redemption fees imposed by the agent.

     In some instances, an authorized agent will not charge any transaction fees
directly to investors in the Funds.  However, for accounting and shareholder
servicing services provided by such agent with respect to Fund share accounts
held on behalf of its customers, the agent may charge a fee (usually a
percentage of the average net assets held in such accounts) for accounting,
shareholder servicing, and distribution services the institution pays with
respect to the underlying Fund shares.  WAM pays any such fees.

Net Asset Value

     Share purchase and redemption orders will be priced at each Fund's NAV next
computed after such orders are received by: (i) Acorn's transfer agent; (ii) a
broker-dealer or other financial services company authorized by Acorn to accept
purchase and redemption orders on the Funds' behalf; or (iii) such authorized
broker-dealer's designee.  Each Fund's NAV is determined only on days on which
the New York Stock Exchange ("NYSE") is open for trading.  The NYSE is regularly
closed on Saturdays and Sundays and on New Year's Day, the third Monday in
January, the third Monday in February, Good Friday, the last Monday in May,
Independence Day, Labor Day, Thanksgiving, and Christmas.  If one of these
holidays falls on a Saturday or Sunday, the NYSE will be closed on the preceding
Friday or the following Monday, respectively.

     Computation of NAV (and the sale and redemption of Fund shares) may be
suspended or postponed during any period when (a) trading on the NYSE is
restricted, as determined by the Securities and Exchange Commission, or that
exchange is closed for other than customary weekend and holiday closings, (b)
the Commission has by order permitted such suspension, or (c) an emergency, as
determined by the Commission, exists making disposal of portfolio securities or
valuation of the net assets of the funds not reasonably practicable.

     For purposes of computing the NAV of a Fund share, a security traded on a
securities exchange, or in an over-the-counter market in which transaction
prices are reported, is valued at the last sale price at the time of valuation.
A security for which there is no reported sale on the 

                                       26
<PAGE>
 
valuation date is valued at the mean of the latest bid and ask quotations or, if
there is no ask quotation, at the most recent bid quotation. Securities for
which quotations are not available and any other assets are valued at a fair
value as determined in good faith by the board of trustees. Money market
instruments having a maturity of 60 days or less from the valuation date are
valued on an amortized cost basis. All assets and liabilities initially
expressed in foreign currencies are converted into U.S. dollars at the mean of
the bid and offer prices of such currencies against U.S. dollars quoted by any
major bank or dealer. If such quotations are not available, the rate of exchange
will be determined in accordance with policies established in good faith by the
board of trustees.

     Trading in the foreign securities of the Funds may take place in various
foreign markets at certain times and on certain days (such as Saturday) when the
NYSE is not open for business and the Funds do not calculate their NAVs.
Conversely, trading in a Fund's foreign securities may not occur at times and on
days when the NYSE is open.  Because of the different trading hours in the
various foreign markets, the calculation of NAV does not take place
contemporaneously with the determinations of the prices of many of the Funds'
foreign securities.  Those timing differences may have a significant effect on a
Fund's NAV.

     Acorn has elected to be governed by Rule 18f-1 under the Investment Company
Act of 1940 pursuant to which it is obligated to redeem shares solely in cash up
to the lesser of $250,000 or 1% of the NAV of a fund during any 90-day period
for any one shareholder.  Redemptions in excess of the above amounts will
normally be paid in cash, but may be paid wholly or partly by a distribution in
kind of securities.  If a redemption is made in kind, the redeeming shareholder
would bear any transaction costs incurred in selling the securities received.

     Due to the relatively high cost of maintaining smaller accounts, Acorn
reserves the right to redeem shares in any account for their then-current value
(which will be promptly paid to the investor) if at any time the account value
falls below $1,000 because of share redemptions.  An investor will be notified
that the value of his account is less than that minimum and allowed at least 30
days to bring the value of the account up to at least $1,000 before the
redemption is processed.  The Declaration of Trust also authorizes Acorn to
redeem shares under certain other circumstances as may be specified by the board
of trustees.

     WAM acts as a shareholder servicing agent for the Reich & Tang Money Funds
(the "Money Funds") in connection with an exchange plan between the Acorn funds
and the Money Funds (the "Switch Plan").  For its services it receives a fee at
the rate of 0.35% of the average annual net assets of each account in a Money
Fund established through the Switch Plan, pursuant to a 12b-1 plan adopted by
the Money Funds.

                           Additional Tax Information

     Each Fund intends to qualify to be taxed as a regulated investment company
under Subchapter M of the Internal Revenue Code (the "Code") so as to avoid
payment of federal income tax on its capital gains and net investment income
currently distributed to its shareholders.

                                       27
<PAGE>

     
     At the time of your purchase, a Fund's NAV may reflect undistributed
income, capital gains, or net unrealized appreciation of securities held by the
Fund.  A subsequent distribution to you of such amounts, although constituting a
return of your investment, will be taxable either as a dividend or capital gain
distribution, whether received in cash or reinvested in additional shares.  For
federal income tax purposes, any distribution that is paid in January but was
declared in October, November or December of the prior calendar year is deemed 
paid in the prior calendar year.

     You will be subject to income tax at ordinary rates on income dividends and
distributions of net short-term capital gains. The Internal Revenue Service 
Restructuring and Reform Act of 1998 eliminated the requirement that capital 
assets be held for more than 18 months in order to be taxed at the lowest rate 
in effect under current law, and instead permits capital assets to be so taxed 
if held for more than one year. This change applies generally to sales 
transactions which occur during taxable years ending after December 31, 1997. 
Distributions of long-term capital gains declared prior to that date will be 
taxed at the rate of 28%, which was in effect prior to the enactment of the new 
legislation. You will be subject to income tax at ordinary rates on income 
dividends and distributions of net short-term capital gain. Distributions of net
long-term capital gains are taxable to you as long-term capital gains (currently
taxed at a maximum rate of 20%) regardless of the length of time you have held 
your shares. Long-term gains are those derived from securities held by the Fund 
for more than one year.      

     You will be advised annually as to the source of distributions for tax
purposes.  If you are not subject to tax on your income, you will not be
required to pay tax on these amounts.  If you realize a loss on the sale of fund
shares held for six months or less, your short-term loss is recharacterized as
long-term to the extent of any long-term capital gain distributions you have
received with respect to those shares.

     Under certain circumstances, a Fund may be required to withhold 31% federal
income tax ("backup withholding") from dividend, capital gain and redemption
payments to you.  Backup withholding may be required if: (a) you fail to
furnish your social security or other tax identification number; (b) you fail to
certify that your social security or tax identification number is correct and
that you are not subject to backup withholding due to the underreporting of
certain income; or (c) the IRS informs the Fund that your tax identification
number is incorrect.

     These certifications are contained in the application that you complete
when you open your Fund account.  Each Fund must promptly pay the IRS all
amounts withheld.  Therefore, it is usually not possible for a Fund to reimburse
you for amounts withheld.  You may, however, claim the amount withheld as a
credit on your federal income tax return.

     Foreign currency gains and losses, including the portion of gain or loss on
the sale of debt securities attributable to foreign exchange rate fluctuations,
are taxable as ordinary income.  If the net effect of these transactions is a
gain, the income dividend paid by the Funds will be increased; if the result is
a loss, the income dividend paid by the Funds will be decreased.

     A portion of the dividends paid by the Funds is expected to be eligible for
the dividends-received deduction.  Capital gain distributions paid from the Fund
are never eligible for this deduction.

     Income received by the Funds from sources within various foreign countries
will be subject to foreign income taxes withheld at the source.  Under the Code,
if more than 50% of the value of a Fund's total assets at the close of its
taxable year comprises securities issued by foreign corporations, the Fund may
file an election with the IRS to "pass through" to its 

                                       28
<PAGE>
 
shareholders the amount of foreign income taxes paid by the Fund. Pursuant to
this election, shareholders will be required to: (i) include in gross income,
even though not actually received, their respective pro rata share of foreign
taxes paid by the Fund; (ii) treat their pro rata share of foreign taxes as paid
by them; and (iii) either deduct their pro rata share of foreign taxes in
computing their taxable income, or use it as a foreign tax credit against U.S.
income taxes (but not both). No deduction for foreign taxes may be claimed by a
shareholder who does not itemize deductions. The Funds do not expect to be able
to "pass through" foreign tax credits.

                             Portfolio Transactions

     Portfolio transactions of the funds are placed with those securities
brokers and dealers that WAM believes will provide the best value in transaction
and research services for each Fund, either in a particular transaction or over
a period of time.  Although some transactions involve only brokerage services,
many involve research services as well.

     In valuing brokerage services, WAM makes a judgment as to which brokers are
capable of providing the most favorable net price (not necessarily the lowest
commission) and the best execution in a particular transaction.  Best execution
connotes not only general competence and reliability of a broker, but specific
expertise and effort of a broker in overcoming the anticipated difficulties in
fulfilling the requirements of particular transactions, because the problems of
execution and the required skills and effort vary greatly among transactions.

     In valuing research services, WAM makes a judgment of the usefulness of
research and other information provided to WAM by a broker in managing each
fund's investment portfolio.  In some cases, the information, e.g., data or
recommendations concerning particular securities, relates to the specific
transaction placed with the broker, but for the greater part the research
consists of a wide variety of information concerning companies, industries,
investment strategy, and economic, financial, and political conditions and
prospects, useful to WAM in advising that fund.

     The reasonableness of brokerage commissions paid by the Fund in relation to
transaction and research services received is evaluated by WAM's staff on an
ongoing basis.  The general level of brokerage charges and other aspects of the
Funds' portfolio transactions are reviewed periodically by the board of
trustees.

     WAM is the principal source of information and advice to the Funds, and is
responsible for making and initiating the execution of investment decisions by
the Funds.  However, the board of trustees recognizes that it is important for
WAM, in performing its responsibilities to the Funds, to continue to receive and
evaluate the broad spectrum of economic and financial information that many
securities brokers have customarily furnished in connection with brokerage
transactions, and that in compensating brokers for their services, it is in the
interest of the Funds to take into account the value of the information received
for use in advising the Funds.  The extent, if any, to which the obtaining of
such information may reduce WAM's expenses in providing management services to
the Funds is not determinable.  In addition, the board of trustees understands
that other clients of WAM might benefit from the information obtained for the
Funds, in the same manner that the Funds might benefit from information obtained
by WAM in performing services to others.

                                       29
<PAGE>
 
     Transactions of the Funds in the over-the-counter market and the third
market are executed with primary market makers acting as principal except where
it is believed that better prices and execution may be obtained otherwise.

     The Funds and WAM each have adopted a code of ethics that, among other
things, regulates the personal transactions in securities of certain officers,
directors, partners, and employees of the Funds and WAM.  Although investment
decisions for the Funds are made independently from those for other investment
advisory clients of WAM, it may develop that the same investment decision is
made for the Funds and one or more other advisory clients.  If the Funds and
other clients purchase or sell the same class of securities on the same day, the
transactions will be allocated as to amount and price in a manner considered
equitable to each.

                                   Custodian

     State Street Bank and Trust Company, P.O. Box 8502, Boston Massachusetts
02266-8502, is the custodian for the Acorn funds.  It is responsible for holding
all securities and cash of the Acorn funds, receiving and paying for securities
purchased, delivering against payment securities sold, receiving and collecting
income from investments, making all payments covering expenses of the funds, and
performing other administrative duties, all as directed by authorized persons of
the funds. State Street does not exercise any supervisory function in such
matters as purchase and sale of portfolio securities, payment of dividends, or
payment of expenses of the Acorn funds.  The Acorn funds have authorized State
Street to deposit certain portfolio securities of the funds in central
depository systems as permitted under federal law.  The Acorn funds may invest
in obligations of the custodian and may purchase or sell securities from or to
State Street.

                              Independent Auditors

     Ernst & Young LLP, Sears Tower, 233 South Wacker Drive, Chicago, Illinois
60606 audits and reports on the Funds' annual financial statements, reviews
certain regulatory reports and the Acorn funds' tax returns, and performs other
professional accounting, auditing, tax, and advisory services when engaged to do
so by the Acorn funds.

                                       30
<PAGE>
 
                     Appendix - Description of Bond Ratings

     A rating of a rating service represents the service's opinion as to the
credit quality of the security being rated.  However, the ratings are general
and are not absolute standards of quality or guarantees as to the
creditworthiness of an issuer. Consequently, WAM believes that the quality of
debt securities in which the funds invest should be continuously reviewed.  A
rating is not a recommendation to purchase, sell, or hold a security, because it
does not take into account market value or suitability for a particular
investor.  When a security has received a rating from more than one service,
each rating should be evaluated independently.  Ratings are based on current
information furnished by the issuer or obtained by the ratings services from
other sources which they consider reliable.  Ratings may be changed, suspended,
or withdrawn as a result of changes in, or unavailability of, such information,
or for other reasons.

     The following is a description of the characteristics of ratings used by
Moody's Investors Service, Inc. ("Moody's") and Standard & Poor's Corporation
("S&P").

Moody's Ratings

     Aaa--Bonds rated Aaa are judged to be the best quality.  They carry the
smallest degree of investment risk and are generally referred to as "gilt-edge".
Interest payments are protected by a large or by an exceptionally stable margin
and principal is secure.  Although the various protective elements are likely to
change, such changes as can be visualized are most unlikely to impair the
fundamentally strong position of such bonds.

     Aa--Bonds rated Aa are judged to be high quality by all standards.
Together with the Aaa group they comprise what are generally known as high grade
bonds.  They are rated lower than the best bonds because margins of protection
may not be as large as in Aaa bonds or fluctuation of protective elements may be
of greater amplitude or there may be other elements present which make the long
term risk appear somewhat larger than in Aaa bonds.

     A--Bonds rated A possess many favorable investment attributes and are to be
considered as upper medium grade obligations.  Factors giving security to
principal and interest are considered adequate but elements may be present which
suggest a susceptibility to impairment sometime in the future.

     Baa--Bonds rated Baa are considered as medium grade obligations, i.e., they
are neither highly protected nor poorly secured.  Interest payments and
principal security appear adequate for the present but certain protective
elements may be lacking or may be characteristically unreliable over any great
length of time.  Such bonds lack outstanding investment characteristics and in
fact have speculative characteristics as well.

     Ba--Bonds rated Ba are judged to have speculative elements; their future
cannot be considered as well assured.  Often the protection of interest and
principal payments may be very moderate and thereby not well safeguarded during
both good and bad times over the future.  Uncertainty of position characterizes
bonds in this class.

                                       31
<PAGE>
 
     B--Bonds rated B generally lack characteristics of the desirable
investment.  Assurance of interest and principal payments or of maintenance of
other terms of the contract over any long period of time may be small.

     Caa--Bonds rated Caa are of poor standing.  Such bonds may be in default or
there may be present elements of danger with respect to principal or interest.

     Ca--Bonds rated Ca represent obligations which are speculative in a high
degree.  Such bonds are often in default or have other marked shortcomings.

S&P Ratings

     AAA--Bonds rated AAA have the highest rating.  Capacity to pay principal
and interest is extremely strong.

     AA--Bonds rated AA have a very strong capacity to pay principal and
interest and differ from AAA bonds only in small degree.

     A--Bonds rated A have a strong capacity to pay principal and interest,
although they are somewhat more susceptible to the adverse effects of changes in
circumstances and economic conditions than bonds in higher rated categories.

     BBB--Bonds rated BBB are regarded as having an adequate capacity to pay
principal and interest.  Whereas they normally exhibit protection parameters,
adverse economic conditions or changing circumstances are more likely to lead to
a weakened capacity to pay principal and interest for bonds in this capacity
than for bonds in higher rated categories.

     BB--B--CCC--CC--Bonds rated BB, B, CCC and CC are regarded, on balance, as
predominantly speculative with respect to the issuer's capacity to pay interest
and repay principal in accordance with the terms of the obligation.  BB
indicates the lowest degree of speculation among such bonds and CC the highest
degree of speculation.  Although such bonds will likely have some quality and
protective characteristics, these are outweighed by large uncertainties or major
risk exposures to adverse conditions.

                                       32
<PAGE>
 
                           PART C  OTHER INFORMATION


Item 24.  Financial Statements and Exhibits

(a)  Financial statements:

  (1)       Financial statements included in Part A of this amendment:

            None

  (2)       Financial statements included in Part B of this amendment:

     (i)    Acorn Fund (incorporated by reference to the following portions of
            Registrant's 1997 Annual Report; a copy of the report was filed with
            the Commission on February 24, 1998 and is not included in this
            amendment):

            Statement of Investments at December 31, 1997

            Report of Independent Auditors

            Statement of Assets and Liabilities at December 31, 1997

            Statement of Operations for the year ended December 31, 1997

            Statement of Changes in Net Assets for the year ended December 31,
            1997

            Notes to financial statements
   
            Acorn Fund (incorporated by reference to the following portions of
            Registrant's June 30, 1998 Semi-Annual Report; a copy of the report
            was filed with the Commission on August 26, 1998 and is not included
            in this amendment):

            Statement of Investments (unaudited) at June 30, 1998

            Statement of Assets and Liabilities (unaudited) at June 30, 1998

            Statement of Operations (unaudited) for the six months ended June 
            30, 1998 and the year ended December 31, 1997

            Statement of Changes in Net Assets (unaudited) for the six months 
            ended June 30, 1998 and the year ended December 31, 1997

            Financial Highlights (unaudited)

            Notes to financial statements    

     (ii)   Acorn International (incorporated by reference to the following
            portions of Registrant's 1997 Annual Report; a copy of the report
            was filed with the Commission on February 24, 1998 and is not
            included in this amendment):

            Statement of Investments at December 31, 1997

            Report of Independent Auditors

            Statement of Assets and Liabilities at December 31, 1997

            Statement of Operations for the year ended December 31, 1997

            Statement of Changes in Net Assets for the year ended December 31,
            1997

            Notes to financial statements
   
            Acorn International (incorporated by reference to the following
            portions of Registrant's June 30, 1998 Semi-Annual Report; a copy of
            the report was filed with the Commission on August 26, 1998 and is
            not included in this amendment):

            Statement of Investments (unaudited) at June 30, 1998

            Statement of Assets and Liabilities (unaudited) at June 30, 1998

            Statement of Operations (unaudited) for the six months ended June 
            30, 1998 and the year ended December 31, 1997

            Statement of Changes in Net Assets (unaudited) for the six months 
            ended June 30, 1998 and the year ended December 31, 1997

            Financial Highlights (unaudited)

            Notes to financial statements     

     (iii)  Acorn USA (incorporated by reference to the following portions of
            Registrant's 1997 Annual Report; a copy of the report was filed with
            the Commission on February 24, 1998 and is not included in this
            amendment):

            Statement of Investments at December 31, 1997

            Report of Independent Auditors

            Statement of Assets and Liabilities at December 31, 1997

            Statement of Operations for the year ended December 31, 1997

                                       1

<PAGE>
 
            Statement of Changes in Net Assets for the year ended December 31,
            1997

            Notes to financial statements
    
            Acorn USA (incorporated by reference to the following portions of
            Registrant's June 30, 1998 Semi-Annual Report; a copy of the report
            was filed with the Commission on August 26, 1998 and is not included
            in this amendment):

            Statement of Investments (unaudited) at June 30, 1998 

            Statement of Assets and Liabilities (unaudited) at June 30, 1998

            Statement of Operations (unaudited) for the six months ended June 
            30, 1998 and the year ended December 31, 1997
           
            Statement of Changes in Net Assets (unaudited) for the six months 
            ended June 30, 1998 and the year ended December 31, 1997

            Financial Highlights (unaudited)

            Notes to financial statements     

  (3)       Financial statements included in Part C of this amendment:

            None

Note:       The following schedules have been omitted for the following reasons:

            Schedules I and III - The required information is presented in the
            statements of investments at December 31, 1997.

            Schedules II, IV and V - The required information is not present.

(b)  Exhibits:

  1.      Agreement and declaration of trust(1)

  2.      Bylaws, as amended October 24, 1997 (exhibit 2.3 to post-effective
            amendment no. 60)(6)

  3.      None

  4.1     Specimen share certificate - Acorn Fund(2)

  4.2     Specimen share certificate - Acorn International(2)

  4.3     Specimen share certificate - Acorn USA(3)
    
  4.4     Specimen share certificates - Acorn Twenty and Acorn Foreign 
          Forty(8)     

  5.1     Investment Advisory Agreement among Acorn Fund, Acorn International,
            Acorn USA and Wanger Asset Management, L.P., dated January 1,
            1998(7)

  5.2     Administration Agreement among Acorn Fund, Acorn International, Acorn
            USA and Wanger Asset Management, L.P., dated January 1, 1998(7)

  5.3     Organizational Expenses Agreement between Acorn Investment Trust and
            Wanger Asset Management, L.P. dated September 3, 1996(7)
    
  5.4     Form of Supplement to the Investment Advisory Agreement between Acorn
            Investment Trust and Wanger Asset Management, L.P., to Acorn Twenty
            and Acorn Foreign Forty, dated ___________, 1998(8)

  5.5     Form of amendment to the Administration Agreement between Acorn
            Investment Trust and Wanger Asset Management, L.P., relating to
            Acorn Twenty and Acorn Foreign Forty, dated ______________, 
            1998(8)     

  6.        Distribution Agreement between Acorn Investment Trust and WAM
            Brokerage Services, L.L.C. dated January 1, 1998(7)

                                       2
<PAGE>
 
    
  6.1     Form of amendment to the Distribution Agreement between Acorn
            Investment Trust and WAM Brokerage Services, L.L.C., relating to
            Acorn Twenty and Acorn Foreign Forty, dated ________, 1998(8)     

  7.      None

  8.1     Custodian contract between the Registrant and State Street Bank and
            Trust Company dated July 1, 1992(1)

  8.2     Letter agreement applying custodian contract(1)

  8.3     Letter agreement applying custodian contract (exhibit 8.1) to Acorn
            USA(7)
    
  8.4     Form of letter agreement applying custodian contract (exhibit 8.1) to
            Acorn Twenty and Acorn Foreign Forty(8)     

  9.      None
    
  10.     Consent of Bell, Boyd & Lloyd     

  11.     Consent of Ernst & Young LLP

  12.     None

  13.     None
    
  14.1    Traditional, Roth and SIMPLE IRA plan booklet including general 
          information, individual retirement plan and custodial agreement and
          individual retirement account disclosure statement, transfer form,
          application form, and designation of beneficiary form (8)

  14.2    Subscription offer IRA application      

  15.     None

  16.1    Computation of performance information - Acorn Fund(1)

  16.2    Computation of performance information - Acorn International(1)

  16.3    Computation of performance information - Acorn USA(5)

  17.1    Financial data schedule - Acorn Fund

  17.2    Financial data schedule - Acorn International

  17.3    Financial data schedule - Acorn USA

_________
(1)  Previously filed. Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 53 to the registrant's registration
statement, Securities Act file number 2-34223 (the "Registration Statement"),
filed on April 30, 1996.

(2)  Previously filed. Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 54 to the Registration Statement,
filed on June 18, 1996.

                                       3
<PAGE>
 
(3)  Previously filed.  Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 55 to the Registration Statement,
filed on September 3, 1996.

(4)  Previously filed.  Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 56 to the Registration Statement,
filed on April 30, 1997.

(5)  Previously filed.  Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 59 to the Registration Statement,
filed on November 25, 1997.

(6)  Previously filed.  Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 60 to the Registration Statement,
filed on December 30, 1997.

(7)  Previously filed.  Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 61 to the Registration Statement,
filed on April 30, 1998.
    
(8)  Previously filed.  Incorporated by reference to the exhibit of the same
number filed in post-effective amendment No. 62 to the Registration Statement,
filed on June 3, 1998.     

Item 25.  Persons Controlled By or Under Common Control with Registrant

     The Registrant does not consider that there are any persons directly or
indirectly controlling, controlled by, or under common control with the
Registrant within the meaning of this item.  The information in the prospectus
under the caption "The Funds in Detail - Organization" and "The Funds in Detail
- - Management" and in the Statement of Additional Information under the caption
"Investment Adviser" is incorporated by reference.

Item 26.  Number of Holders of Securities
    
     At September 30, 1998, there were 56,816 record holders of Registrant's
shares of beneficial interest of the series designated Acorn Fund; 59,049
record holders of Registrant's shares of beneficial interest of the series
designated Acorn International; and 8,986 record holders of Registrant's
shares of beneficial interest of the series designated Acorn USA.     

Item 27.  Indemnification

     Article VIII of the Agreement and Declaration of Trust of the Registrant
(exhibit 1) provides in effect that Registrant shall provide certain
indemnification of its trustees and officers.  In accordance with Section 17(h)
of the Investment Company Act of 1940, that provision shall not protect any
person against any liability to the Registrant or its shareholders to which he
would otherwise be subject by reason of willful misfeasance, bad faith, gross
negligence or reckless disregard of the duties involved in the conduct of his
office.

     Insofar as indemnification for liabilities arising under the Securities Act
of 1933 (the "Securities Act") may be permitted to trustees, officers and
controlling persons of the Registrant pursuant to the foregoing provisions, or
otherwise, the Registrant has been advised that in the opinion of the Securities
and Exchange Commission such indemnification is against public policy as
expressed in the Securities Act and is, therefore, unenforceable.  In the event
that a claim for indemnification against such liabilities (other than the
payment by the Registrant of expenses incurred or paid by a trustee, officer or
controlling person of the Registrant in the successful defense of any action,
suit or proceeding) is asserted by such trustee, officer or controlling person
in connection with the securities being registered, the Registrant will, unless
in the opinion of its counsel the matter has been settled by controlling
precedent, submit to a 

                                       4
<PAGE>
 
court of appropriate jurisdiction the question whether such indemnification by
it is against public policy as expressed in the Securities Act and will be
governed by the final adjudication of such issue.

     Registrant, its trustees and officers, its investment adviser and persons
affiliated with them are insured under a policy of insurance maintained by
Registrant and its investment adviser, within the limits and subject to the
limitations of the policy, against certain expenses in connection with the
defense of actions, suits or proceedings, and certain liabilities that might be
imposed as a result of such actions, suits or proceedings, to which they are
parties by reason of being or having been such trustees or officers. The policy
expressly excludes coverage for any trustee or officer whose personal
dishonesty, fraudulent breach of trust, lack of good faith, or intention to
deceive or defraud has been finally adjudicated or may be established or who
willfully fails to act prudently.

Item 28.  Business and Other Connections of Investment Adviser

     The information in the prospectus under the caption "The Funds in Detail -
Management" and in the Statement of Additional Information under the caption
"Investment Adviser" is incorporated by reference.  Neither Wanger Asset
Management, L.P. nor its general partner has at any time during the past two
years been engaged in any other business, profession, vocation or employment of
a substantial nature either for its own account or in the capacity of director,
officer, employee, partner or trustee.

Item 29.    Principal Underwriters

     WAM Brokerage Services, L.L.C. also acts as principal underwriter for
Wanger Advisors Trust.

<TABLE>
<CAPTION>
       Name                     Positions and Offices with       Positions and Offices with
                                         Underwriters                      Registrant
<S>                             <C>                              <C>
Bruce H. Lauer                  President                        Vice President and Treasurer
Merrillyn J. Kosier             Vice President and Secretary     Senior Vice President and
                                                                 Secretary
</TABLE>

The principal business of each officer of WAM Brokerage Services, L.L.C. is 227
West Monroe Street, Suite 3000, Chicago, Illinois 60606.

Item 30.  Location of Accounts and Records

          Bruce H. Lauer, Vice President and Treasurer
          Acorn Investment Trust
          227 West Monroe Street, Suite 3000
          Chicago, Illinois  60606

Item 31.  Management Services

          None

                                       5
<PAGE>
 
Item 32.  Undertakings

          (a)     Not applicable.

          (b)     Registrant undertakes to furnish each person to whom a
                  prospectus is delivered with a copy of the Registrant's latest
                  annual report to shareholders, upon request and without
                  charge.

                                       6
<PAGE>
 
                                   SIGNATURES
    
     Pursuant to the requirements of the Securities Act of 1933 and the
Investment Company Act of 1940, the registrant certifies that it meets all of
the requirements for effectiveness of this registration statement under Rule
485(b) under the Securities Act and has duly caused this amendment to the
registration statement to be signed on its behalf by the undersigned, thereunto
duly authorized, in Chicago, Illinois on October 15, 1998.     

                                    ACORN INVESTMENT TRUST


                                    By /s/Ralph Wanger
                                       ---------------
                                       Ralph Wanger, President

     Pursuant to the requirements of the Securities Act of 1933, this amendment
to the registration statement has been signed below by the following persons in
the capacities and on the dates indicated.

<TABLE>    
<CAPTION>
         Name                   Title                   Date
         ----                   -----                   ----
<S>                      <C>                         <C>
/s/Irving B. Harris      Trustee and chairman     )
- -----------------------                           )
Irving B. Harris                                  )
                                                  )
/s/Leo A. Guthart        Trustee                  )
- -----------------------                           )
Leo A. Guthart                                    )
                                                  )
/s/Jerome Kahn, Jr.      Trustee                  )
- -----------------------                           )
Jerome Kahn, Jr.                                  )
                                                  )
/s/David C. Kleinman     Trustee                  )
- -----------------------                           )
David C. Kleinman                                 )
                                                  )
/s/James H. Lorie        Trustee                  )
- -----------------------                           )
James H. Lorie                                    )
                                                  )
/s/Charles P. McQuaid    Trustee                  )  October 15, 1998
- -----------------------                           )
Charles P. McQuaid                                )
                                                  )
                         Trustee                  )
- -----------------------                           )
Roger S. Meier                                    )
                                                  )
/s/Adolph Meyer, Jr.     Trustee                  )
- -----------------------                           )
Adolph Meyer, Jr.                                 )
                                                  )
/s/Ralph Wanger          Trustee and President    )
- -----------------------  (principal executive     )
Ralph Wanger             officer)                 )
                                                  )
/s/Bruce H. Lauer        Treasurer (principal     )
- -----------------------  financial and accounting )
Bruce H. Lauer           officer)                 )
</TABLE>     
<PAGE>

                  Index of Exhibits Filed with this Amendment
                  -------------------------------------------

<TABLE>
<CAPTION>
   
Exhibit
Number                              Exhibit
- ------                              -------
<C>              <S>
10.              Opinion and consent of Bell, Boyd & Lloyd
11.              Consent of Ernst & Young LLP
14.1             Traditional, Roth and Simple IRA plan booklet
14.2             Subscription offer IRA application
17.1             Financial data schedule - Acorn Fund
17.2             Financial data schedule - Acorn International
17.3             Financial data schedule - Acorn USA     
</TABLE>


<PAGE>
 
                                                                      Exhibit 10

                               BELL, BOYD & LLOYD
                           Three First National Plaza
                       70 West Madison Street, Suite 3300
                          Chicago, Illinois 60602-4207

                                  312 372 1121
                               Fax: 312 372 2098


                                October 15, 1998



     As counsel for Acorn Investment Trust (the "Trust"), we consent to the
incorporation by reference of our opinion dated June 2, 1998 as an exhibit to
post-effective amendment no. 63 to the registration statement of the Trust,
Securities Act File No. 2-34223, on Form N-1A.  In giving this consent we do not
admit that we are in the category of persons whose consent is required under
section 7 of the Act.


October 15, 1998


                                /s/ Bell, Boyd & Lloyd

<PAGE>
 
                                                                      Exhibit 11

                        CONSENT OF INDEPENDENT AUDITORS

We consent to the references to our firm under the caption "Independent
Auditors" and to the use of our report dated February 4, 1998 on the 1997
financial statements of the Acorn Investment Trust (comprising Acorn Fund, Acorn
International and Acorn USA) and its incorporation by reference in the
Registration Statement (Form N-1A) and in the related Prospectus and Statement
of Additional Information, filed with the Securities and Exchange Commission in
this Post-Effective Amendment No. 63 to the Registration Statement under the
Securities Act of 1933 (Registration No. 2-34223) and in the Amendment No. 38 to
the Registration Statement under the Investment Company Act of 1940
(Registration No. 811-1829).

                                               /s/ Ernst & Young LLP



Chicago, Illinois
October 15, 1998

<PAGE>
                                                                    Exhibit 14.1

 
This booklet contains important legal information regarding Traditional IRAs,
SEP-IRAs and Roth IRAs. We are required to provide this to you for the purpose
of assuring that you are informed and understand the nature of an Individual
Retirement Account. Please read this booklet carefully before investing in an
Acorn IRA and keep it on file for future reference.



The Acorn Family of Funds
IRA Disclosure Statement
Custodial Agreement for a Traditional or SEP-IRA
Custodial Agreement for a Roth IRA


Managed by Wanger Asset Management, L.P.
<PAGE>
 
Contents


<TABLE>
<CAPTION>
 
<S>                                                 <C>
IRA Disclosure Statement                             1
 
Custodial Agreement for a Traditional or SEP-IRA    12
 
Custodial Agreement for a Roth IRA                  21
</TABLE>
<PAGE>
 
Acorn Investment Trust
Individual Retirement Account Disclosure Statement

We are required to give you this Disclosure Statement for the purpose of
assuring that you are informed and understand the nature of an Individual
Retirement Account ("IRA"). This disclosure statement explains the rules
governing IRAs.

Your Right to Revoke this IRA. You may revoke this IRA at any time within seven
days after the later of the date you received this Disclosure Statement or the
day you established this IRA. For purposes of revocation, it will be assumed
that you received the Disclosure Statement no later than the date of your check
or transfer direction with which you opened your IRA. If you did not receive the
Disclosure Statement until a later date, your notice of revocation should state
the date on which the Disclosure Statement was received. To revoke the IRA, you
must either mail or deliver a notice of revocation to the following address:

 State Street Bank and Trust Company
 Attention: Acorn Family of Funds
 P.O. Box 8502
 Boston, MA 02266-8502

     If a notice of revocation is mailed, it will be deemed mailed on the date
of the postmark (or if sent by certified or registered mail, the date of
certification or registration) if it is deposited in the mail in the United
States, first class postage prepaid and properly addressed. If you revoke your
IRA, you are entitled to a return of the entire amount contributed.

I. Types of IRAs; Eligibility

In General. An IRA is a trust or custodial account established in the United
States for the exclusive benefit of an individual and his or her beneficiaries
and which, under Section 408(a) of the Internal Revenue Code, meets the
following requirements: annual contributions are limited as described below; the
trustee or custodian is a bank or other approved financial institution; no part
of the IRA can be invested in life insurance contracts; the individual's
interest in the IRA is nonforfeitable; the IRA's assets cannot be commingled
with other property except for certain permitted common funds; and minimum
distributions are required as described below. There are several types of IRAs,
as follows: (1) a "Traditional IRA" to which you may make contributions for
yourself or for your spouse, which may be partially or fully tax-deductible, as
described below; (2) a "Roth IRA" to which you may also make nondeductible
annual contributions, and the distributions from which may be excludible from
your taxable income; (3) a "Rollover IRA" which you can establish to receive
assets from a qualified plan, annuity or another IRA; (4) a "SEP-IRA" (which is
also known as a Simplified Employee Pension) which your employer can establish
for you; and (5) a "SIMPLE-IRA" (also known as a Salary Incentive Match Plan
IRA) which an employer can use for a salary reduction plan. The following is a
general description of the rules which apply to each of these types of IRAs and
who is eligible to establish them.

A. Traditional IRAs. You may contribute up to the lesser of $2,000 or 100% of
your compensation if you have not reached age 70-1/2 during the taxable year.
You may make this contribution even if you or your spouse is an active
participant in a qualified employer plan. However, as explained below, the
amount of the contribution that is deductible for federal income tax purposes
may be limited. Compensation includes wages, salary, commissions, bonuses, tips,
etc., and also includes taxable alimony or separate maintenance payments.
Compensation does not include income from interest, dividends or other earnings
or profits from property, amounts not includible in your gross income, or
deferred compensation.

     Your spouse may also establish and contribute to an IRA, even if he or she
has less than $2,000 in compensation for the year, provided that you and your
spouse file a joint income tax return for the year. Under such an arrangement,
you and your spouse may qualify for a total contribution equal to the lesser of
$4,000 or 100% of your combined compensation for the taxable year. You can
determine how to divide the contribution between the two accounts but you cannot
contribute more than $2,000 annually into either one. While you cannot
contribute to your IRA in the taxable year in which you reach 70-1/2, you can
still contribute to your spouse's IRA if he or she has not reached 70-1/2. A
spousal IRA does not involve the creation of a joint account. The account of
each spouse is separately owned and treated independently from the account of
the other spouse.

                                       1
<PAGE>
 
IRA Disclosure Statement, continued


B. Roth IRAs. In general, the same limits that apply to contributions to
Traditional IRAs also apply to Roth IRAs, with the following differences. First,
you can make a contribution to a Roth IRA even after you have attained the age
of 70-1/2. Second, only a taxpayer whose adjusted gross income is below certain
levels is eligible to contribute to a Roth IRA. A single taxpayer can make a
full $2,000 contribution in a year if his adjusted gross income is not more than
$95,000. Married taxpayers who file a joint return can make a full $4,000
contribution if their combined adjusted gross income is not more than $150,000.
Partial contributions are permitted for a single taxpayer whose adjusted gross
income is between $95,000 and $110,000, or for married taxpayers who file a
joint return and whose adjusted gross income is between $150,000 and $160,000. A
married taxpayer who files an individual return can make a partial contribution
if his/her adjusted taxable income is less than $10,000. These partial
contributions are calculated in the same manner as the limitation on the
deductibility of contributions to a Traditional IRA, including the adjustments
to adjusted gross income, as described under Contributions N Deductible
Contributions on page 5.

     A single $2,000 limit ($4,000 for married taxpayers filing joint returns)
applies to contributions to both Traditional IRAs and Roth IRAs. Thus, a single
taxpayer who is otherwise eligible to contribute to both a Traditional IRA and a
Roth IRA can contribute a total of $2,000, which he or she can divide between
the Traditional and the Roth IRA in any manner. A married couple filing a joint
return can similarly divide their maximum $4,000 total contribution between
Traditional and Roth IRAs. These rules apply regardless of whether the
contributions to the Traditional IRA are deductible.

     If you make a contribution to either a Traditional IRA or a Roth IRA for a
year, you may transfer the contribution, including all income, to the other type
of IRA prior to the due date for your tax return, in which case the contribution
will be treated as if you had made it directly to the transferee IRA. For this
purpose, the due date of your tax return includes any extension of time, even
though extensions are not included for purposes of making the original
contribution.

C. Rollover IRAs. All or a portion of certain distributions from qualified
retirement plans, annuities and other IRAs may be "rolled over" tax-free without
regard to the limits on annual contributions to an IRA, but no deduction is
allowed with respect to such a contribution. There are three basic types of
rollovers: rollovers from a qualified pension or profit-sharing plan, rollovers
from another IRA, and rollovers from a tax-sheltered annuity. All distributions
must be rolled over within 60 days after you receive the distribution to receive
tax-free treatment.

From a Qualified Plan. In general, you may roll over to a Traditional IRA any
portion of a distribution that you receive from a qualified employer-sponsored
pension or profit-sharing plan (including a 401(k) plan), except that you cannot
roll over (1) one of a series of substantially equal periodic payments (such as
an annuity), (2) a minimum distribution required to be made after you reach the
age of 70-1/2, (3) the portion of a distribution that represents the return of
your own after-tax contributions or (4) beginning in 1999, a hardship withdrawal
from a 401(k) plan. If you receive a distribution of property rather than cash,
you can sell the property and roll over the sale proceeds, as long as you
complete the rollover within 60 days from the original date of distribution.

     If you make a rollover from a qualified employer plan to an IRA, you may in
turn, under certain circumstances, make a rollover from the IRA into the
qualified plan of a subsequent employer. To preserve that right, however, you
must keep the rollover IRA separate from any other IRA you may have, since you
cannot make a rollover to an employer plan from an IRA to which you have made
yearly contributions.

     Instead of receiving a distribution from a qualified plan and rolling it
over, you may also direct the trustee or custodian of any qualified retirement
plan to transfer a distribution from the plan directly to an IRA. If a
distribution from a plan can be rolled over, the plan is required by law to
transfer the distribution directly to an IRA, or another employer's plan, if you
so direct. If you do not direct the distribution to be transferred directly to
an IRA or another plan, the plan making the distribution will be required to
withhold 20% of the distribution for the payment of income taxes, even if you
subsequently roll over the distribution.

                                       2
<PAGE>
 
     Rollover amounts you receive from a qualified employer plan may not be
deposited in your spouse's IRA, but if you should die while still a participant
in a qualified plan, in certain cases your spouse may be allowed to make a tax-
free rollover to an IRA. The amount of the death payout rolled over by a spouse
into an IRA may not subsequently be rolled over into another employer's
qualified plan or annuity. Beneficiaries other than a spouse are not allowed to
roll over distributions they receive after your death.

     Money from an employer plan cannot be rolled over into a Roth IRA, but you
may be eligible to convert a Rollover IRA into a Roth IRA.

From Another IRA. In general, any distribution or withdrawal that you receive
from an IRA can be rolled over into another IRA within 60 days, except that (1)
you cannot roll over the minimum distributions you are required to receive after
age 70-1/2, (2) you can only make a rollover from one IRA to another once in any
twelve-month period, (3) a distribution from a SIMPLE-IRA that is made within
the first two years after you first begin to participate in the SIMPLE-IRA can
only be rolled over to another SIMPLE-IRA, and (4) special rules apply to
rollovers to and from Roth IRAs as described below. You may also request the
trustee or custodian of an IRA to make a direct transfer to the trustee or
custodian of another IRA. Such direct transfers are not limited to one per
twelve-month period. Unlike the trustees of qualified retirement plans, trustees
of IRAs are not legally required to make direct transfers, but most of them do.
Your spouse may generally roll over distributions that he or she receives from
your IRA after your death, but no beneficiaries other than your spouse may do
so.

Tax Sheltered Annuities. Tax-sheltered annuity plans, sometimes called "403(b)
plans", are retirement benefits offered by certain governmental and not-for-
profit employers, such as schools and hospitals. If you receive a distribution
from a tax-sheltered annuity plan other than in the form of an annuity, it may
generally be rolled over into an IRA under rules similar to those that apply to
distributions from qualified employer plans, as described above (including the
prohibition on rollovers of hardship withdrawals beginning in 1999). As with a
rollover distribution from an employer plan, you should keep a rollover from a
tax-sheltered annuity plan in a separate IRA account and not make any other
contributions to it (including rollovers from other types of plans) if you wish
to preserve the right to roll it over to another tax-sheltered annuity plan in
the future. Distributions from other types of governmental retirement plans may
or may not be eligible for a rollover depending on whether the employer has
chosen to comply with IRS guidelines. Distributions from voluntary deferred
compensation plans maintained by government and not-for-profit employers,
sometimes known as "Section 457 plans", are not eligible for a rollover to an
IRA.

Rollovers to and from Roth IRAs. The rules described above generally apply to
rollovers to any type of IRA other than a Roth IRA, regardless of whether it was
originally established as a Rollover IRA or as a Traditional IRA, SEP-IRA, or
SIMPLE-IRA. Generally speaking, tax-free rollovers to a Roth IRA can only be
made from another Roth IRA, and a distribution from a Roth IRA can only be
rolled over to another Roth IRA (except for transfers of contributions made
before the due date for filing your tax return for the year, as described
above). However, you can roll over a distribution from a Traditional IRA (or any
other type of IRA that is not a Roth IRA) to a Roth IRA, provided that your
adjusted gross income for the year (determined prior to the rollover) does not
exceed $100,000. The same $100,000 limit applies to both single taxpayers and
married taxpayers filing joint returns; a married taxpayer who files a separate
return cannot roll over a distribution from a non-Roth IRA into a Roth IRA. A
rollover from a non-Roth IRA to a Roth IRA is not tax-free; the owner of the
non-Roth IRA must include the distribution in taxable income as if it were not
rolled over. However, if a rollover is made in 1998, one-fourth of the
distribution is included in income in the years 1998 through 2001. After 1998,
the entire amount must be included in income in the year received. In addition,
rollovers from a non-Roth IRA into a Roth IRA are not subject to the 10% penalty
tax described below, and are not taken into account in determining the
taxpayer's eligibility to make annual contributions to the Roth IRA.

                                       3
<PAGE>
 
IRA Disclosure Statement, continued


     If you make a rollover from a Traditional IRA to a Roth IRA in 1998, you
may elect to have the entire amount of the rollover included in your 1998 income
rather than spread over four years as described above. However, even if you
elect to spread the income over four years, taxability of the amount rolled over
may be accelerated to the extent you make withdrawals during the four year
period, and may also be subject to the 10% penalty tax discussed below.
Taxability of the rollover will also be accelerated and reported in your final
tax return if you die during the four year period, unless your spouse is your
sole beneficiary and elects to continue to report the income over the remainder
of the four year period.

     Strict requirements must be met to qualify for tax-free rollover treatment.
You should consult your personal tax adviser regarding rollovers to and from
your IRA.

D. Simplified Employee Pension (SEP-IRAs). An employer may adopt a SEP-IRA and
contribute to your SEP-IRA even if you are covered by another retirement plan.
The maximum contribution is 15% of your compensation (computed without regard to
the contribution) or $24,000 (or such other amount as may be prescribed by the
Secretary of the Treasury), whichever is less. The contributions are deductible
by the employer and are generally not includible in your income until you
receive distributions. You may also be able to elect to have your salary reduced
by up to $10,000 for 1998 (or such higher amount as is specified from time to
time by the Secretary of the Treasury) and to contribute the reduction to your
SEP-IRA, but only if prior to 1997 your employer had established a special type
of SEP-IRA (called a SAR-SEP) that permitted such elections. SAR-SEPs were
replaced in 1997 by SIMPLE-IRAs (discussed below), and new SAR-SEPs are not
permitted. To establish a SEP-IRA, your employer must sign a SEP-IRA plan
agreement and provide you with a copy of the agreement as well as certain
information concerning the rules applicable to such plans. Your employer can
satisfy these requirements by using Form 5305-SEP, which is issued by the
Internal Revenue Service. If you are self-employed, you may establish a SEP-IRA
for your own benefit, but you may also have to cover any other employees you
have.

E. Salary Incentive Match Plan (SIMPLE-IRAs). Before 1997, employers with up to
25 eligible employees could allow employees to elect to have a portion of their
pay withheld and contributed to a special type of SEP-IRA, called a "salary
reduction SEP", or SAR-SEP. SAR-SEPs were abolished in 1997, and a new type of
IRA, called a SIMPLE-IRA has been established instead. Although new SAR-SEPs can
no longer be established, SAR-SEPs that were in existence on December 31, 1996,
can remain in existence and continue to receive contributions in future years,
including contributions for new employees. Employers with up to 100 eligible
employees who have no other retirement plans can establish SIMPLE-IRAs.

     If you wish to establish a SIMPLE-IRA for your employees, you must give all
eligible employees notice of their right to elect to defer part of their
compensation, and comply with certain other notice requirements. The Acorn IRA
Application and Transfer Form cannot be used to establish a SIMPLE-IRA. Call 1-
800-962-1585 to request the necessary forms.

F. Education IRAs.

Beginning in 1998, you may establish an Education IRA for any beneficiary who is
under the age of 18.

     The rules governing Education IRAs are very different from the rules
governing other types of IRAs. In reading this Disclosure Statement, you should
not assume that any of the general discussion of IRAs applies to Education IRAs.
Acorn has a separate Education IRA booklet with the Disclosure Statement,
Custodial Agreement and forms to open an Education IRA. Call 1-800-962-1585 for
an Education IRA booklet.

II. Contributions

In General. As explained in this part, the amount of your contributions to a
Traditional IRA that you can deduct is subject to limits. All contributions and
transfers to your Acorn IRA must be in cash. Contributions to your or your
spouse's Traditional or Roth IRA may be made up to the due date for filing your
tax return for the taxable year (excluding extensions thereof) even if you file
before the due date. In making contributions, you must indicate the tax year to
which the contribution applies. If no tax year is designated,

                                       4
<PAGE>
 
the custodian will assume that the contribution is intended to apply to the
calendar year in which it is received. The time limit for designating the
applicable tax year is April 15. If you are the beneficiary of an IRA following
the death of the IRA owner, you may not make any additional contributions to
that IRA unless you are the surviving spouse of the IRA owner.

     Contributions made by an employer to your SEP-IRA or SIMPLE-IRA for a
calendar year may be made no later than the due date of your employer's tax
return (including extensions). In making an SEP-IRA or SIMPLE-IRA contribution,
the tax year to which the contribution relates must also be specified or it will
be deemed to relate to the calendar year in which it is received. In an SEP-IRA
or SIMPLE-IRA, this designation of the tax year of a contribution must be made
by the due date for contributions described above.

Deductible Contributions. If you are single and are not an "active participant"
in a retirement plan maintained by your employer, you can deduct the full amount
of your Traditional IRA contribution up to the lesser of $2,000 or 100% of your
compensation for the year. If you are married, you can deduct the full amount of
your Traditional IRA contribution provided that neither you nor your spouse is
an "active participant" in a retirement plan maintained by your respective
employers. These plans include qualified pension, profit-sharing, stock bonus or
money purchase plans, 401(k) plans, SEP-IRAs and SIMPLE-IRAs, qualified annuity
plans, tax-sheltered annuities and custodial accounts and governmental
retirement plans (other than certain plans for reserve members of the armed
forces and volunteer firemen, and certain deferred compensation plans commonly
known as "Section 457 plan"). In general, you are considered to be an active
participant in a plan if an employer contribution or forfeiture was credited to
your account during the year in the case of a defined contribution plan or if
you have met the minimum age and service requirements, in the case of a defined
benefit plan (even if you don't actually accrue a benefit during the year). You
are considered to be an active participant in a plan if you make a contribution
to the plan during a year even if your employer does not. For active
participation, it does not matter whether any interest you have in a plan is
vested or unvested.

     If you or your spouse is an active participant in a plan, the amount of the
deduction you can claim for a Traditional IRA contribution is reduced or totally
denied depending upon the amount by which your adjusted gross income for the
year exceeds the "applicable dollar amount." For 1998 contributions, the
applicable dollar amounts are $30,000 for single people and $50,000 for married
couples if the spouse who is making the contribution is an active participant.
These applicable dollar amounts are increased by an additional $1,000 for each
year from 1999 through 2002. If the spouse making the contribution is not an
active participant, but the other spouse is an active participant, the
applicable dollar amount for the spouse who is not an active participant is
$150,000. The applicable dollar amount for married individuals who file separate
tax returns is $0, unless they live apart for the entire year, in which case the
applicable dollar amount is the same as for single individuals.

     If your adjusted gross income exceeds your applicable dollar amount by more
than $10,000, you may not deduct any portion of your IRA contribution. However,
if it is between $0 and $10,000 more than your applicable dollar amount, you can
claim a tax deduction for part of your contribution. To determine the amount of
the deduction, follow these steps. First, determine the amount of the
contribution you can make. If, for example, you have compensation in excess of
$2,000 you could make a $2,000 contribution to your Traditional IRA. Next,
subtract the applicable dollar amount from your adjusted gross income. If you
are single and your adjusted gross income for 1998 is $35,000, the difference
would be $5,000. Next, divide this difference by $10,000. In this example,
$5,000/$10,000 equals 50%. Accordingly, the maximum contribution to a
Traditional IRA that you can deduct is 50% of $2,000, or $1,000. If the
deduction limitation is not a multiple of $10, round the deduction to the next
higher $10. If your adjusted gross income does not exceed $40,000 if you are
single, $60,000 if you are married and an active participant, or $160,000, if
you are married to an active participant, you can deduct $200 regardless of how

                                       5
<PAGE>
 
IRA Disclosure Statement, continued


the computation comes out. (These amounts apply to 1998 contributions; after
1998, increase each limit other than the $160,000 limit by $1,000 per year.)

     For this purpose, your "adjusted gross income" is the amount shown on the
appropriate line of your tax return, before you deduct your Traditional IRA
contribution, plus the following amounts that are tax-exempt: the proceeds of
any US savings bonds that you cash in to pay college expenses, any adoption
expenses paid by your employer, and amounts paid to you while working outside
the US. Married persons who file separate returns are treated as unmarried for
purposes of these rules if they did not live together at any time during the
year.

Nondeductible Contributions. Even though you may not be entitled to claim a
deduction for contributions to your Traditional IRA, you are still allowed to
make the contributions to the extent described in "Types of IRAs" above. To the
extent that the amount of your contribution exceeds the deduction limit, it is
considered a nondeductible contribution. Earnings on these contributions are not
taxed until distributed, just like the earnings on deductible contributions. It
may therefore be worthwhile making nondeductible contributions.

   You are required to report the amount of your nondeductible contributions on
Form 8606 and attach it to your income tax return. You may be liable for a tax
penalty of $50 if you fail to file Form 8606, or $100 if you overstate the
amount of your nondeductible contributions.

   Contributions to a Roth IRA or Education IRA are not deductible under any
circumstances.

III. Investment and Holding of Contributions

Contributions to your IRA, and the earnings thereon, are invested at your
election in shares of any Acorn fund, each a series of Acorn Investment Trust, a
no-load mutual fund managed by Wanger Asset Management, L.P., or in the shares
of any other mutual fund made available by Acorn for investment.

   All the funds eligible for investment by your IRA are available in a
telephone exchange plan. In order to enroll in the exchange plan, indicate your
election on the IRA Application. When your exchange plan is established, you can
request a prospectus for any eligible fund and you will then be able to exchange
by telephoning State Street Bank and Trust Company. IRA planholders may not use
check-writing redemption privileges offered by the money fund.

   If you wish to add to your IRA plan by putting money into an eligible fund
other than one of the Acorn Funds, please call Acorn for instructions.

   The assets in your account are held in a custodial account exclusively for
your benefit and the benefit of such beneficiaries as you may designate in
writing delivered to the Custodian. The balance in your IRA represents a
separate account which is clearly identified as your property and generally may
not be combined for investment with the property of another individual. Your
right to the entire balance in your account is nonforfeitable. No part of the
assets of your account may be invested in life insurance contracts or in
collectibles such as works of art, antiques, coins, stamps, etc.

IV. Distributions From Your IRA

Distributions During Your Life. The law permits distributions to be made from an
IRA without penalty at any time after you attain age 59 1/2, and requires that
distributions commence (except from a Roth IRA) no later than April 1 following
the calendar year in which you attain age 70 1/2. Distributions may be in the
form of a single payment or, in accordance with regulations, in substantially
equal monthly, quarterly or annual payments over your life or the joint lives of
you and your designated beneficiary, or over a period certain not extending
beyond your life expectancy or the joint and last survivor life expectancy of
you and your designated beneficiary. However, if your beneficiary is not your
spouse, the law imposes an additional requirement called the minimum
distribution incidental benefit requirement. In general, this requirement puts a
further limit on the maximum payout period. This further limit is based on a
table in the income tax regulations, and if this limit applies to you, you
should consult your tax adviser to determine your minimum distribution.

   In general, your life expectancy, your surviving spouse's life expectancy
after your death, and your and your

                                       6
<PAGE>
 
spouse's joint and last survivor life expectancies will all be recalculated
each year based upon your (and your spouse's, if applicable) age attained during
that year. However, you can also elect to have your (and your spouse's) life
expectancies fixed in the year in which distributions are required to begin,
which may be advantageous in some circumstances. On the other hand, if your
beneficiary is someone other than your surviving spouse, your and your
beneficiary's joint and last survivor life expectancy will ordinarily not be
recalculated each year, although you may elect to have it recalculated. Each of
the elections described above must be made before the date on which
distributions are required to commence, and will be irrevocable after that date.
You should consult a qualified tax adviser to determine whether you should make
any of these elections.

     If you direct distributions over your life or the joint lives of you and
your designated beneficiary, the Custodian will purchase an immediate annuity
contract from an insurance company you choose with your IRA and your payments
will be made under the annuity. You must provide a completed annuity application
from the insurance company of your choosing. Any distribution instructions must
specify the reason for the distribution. Examples of such reasons are: premature
distributions (i.e. distributions before age 59 1/2), rollovers, disability,
death, normal (59 1/2 or over), excess contribution returns and other.

Distributions After Your Death. If you die on or after the April 1 following the
year in which you reach age 70 1/2, the balance of your IRA (other than a Roth
IRA) must be distributed to your designated beneficiary at least as rapidly as
under the method of distribution in effect before your death.

     If you die before the April 1 following the year in which you reach age
70 1/2, the entire balance of the account (including a Roth IRA) must be
distributed by December 31 of the year in which the 5th anniversary of your
death occurs. This rule also applies to a Roth IRA, regardless of your age at
death. However, distribution need not be made within this 5-year period if your
beneficiary receives payments over a period measured by his or her life or life
expectancy beginning no later than December 31 of the year following the year in
which you die. If the beneficiary is your spouse, those installment payments
from a Traditional IRA don't have to begin until the later of December 31 of the
year following the year in which you die or December 31 of the year in which you
would have reached age 70 1/2. In addition, a distribution need not be made
within 5 years of your death if your spouse is your beneficiary and he or she
elects to treat the entire interest in either a Traditional or Roth IRA (or the
remaining part of such interest, if distribution has already begun) as his or
her own IRA subject to the normal IRA distribution requirements. In such a case,
your spouse will be considered to be the covered individual under the IRA. If
you die before the entire IRA has been distributed to you and your spouse is not
your beneficiary, no additional cash contributions or rollover contributions may
be accepted by the IRA.

V. Income and Penalty Taxes

Income Tax Treatment of IRAs. Income tax on deductible IRA contributions and
earnings on both deductible and nondeductible IRA contributions are generally
deferred until you receive distributions. If you have made both deductible and
nondeductible contributions to IRAs you maintain, a portion of each distribution
you receive from any IRA (whether or not it is the one to which you made
nondeductible contributions) will be considered to be a return of nondeductible
contributions and therefore not included in your income for tax purposes. The
balance of each distribution will be taxed as ordinary income regardless of its
original source. The amount of any distribution which is considered to be a
return of nondeductible contributions (and therefore not taxed) is determined by
multiplying the amount of the distribution by a fraction. The numerator of the
fraction is the aggregate amount of nondeductible contributions you have made to
all of your IRAs over the years and the denominator is the balance in all your
IRAs at the end of the year (after adding back any distributions you received
during the year). The aggregate amount which can be excluded from income for all
years cannot exceed the amount of nondeductible contributions that you made in
those years. You must attach Form 8606

                                       7
<PAGE>
 
IRA Disclosure Statement, continued

to your tax return for any year in which you receive distributions if you have
made any nondeductible contributions to an IRA.

     Taxable distributions from your account are taxed as ordinary income
regardless of their original source. They are not eligible for special tax
treatment that may apply to lump sum distributions from qualified employer
plans.

Nontaxable Distributions from Roth IRAs.

Unlike most IRAs, "qualified distributions" from a Roth IRA are not subject to
tax at all, either on the original contribution or on any accumulated income. In
order to be a "qualified distribution", a distribution from a Roth IRA (1) may
not be made until after the end of the fifth year beginning with the first year
in which either you or your spouse first make a contribution to a Roth IRA, and
(2) must either be made after you attain the age of 59 1/2, after you have
become permanently disabled, to your beneficiary after your death, or must be
used to pay qualified first time homebuyer expenses, as described in the section
on penalty taxes below. The five year requirement is satisfied five years after
you or your spouse make your first contribution to any Roth IRA, even if it is
not the same Roth IRA that you are receiving the distribution from. If you
receive distributions from a Roth IRA that are not qualified distributions, such
distributions will first be treated as nontaxable returns of your contributions,
and the excess will be taxed as ordinary income.

Penalty Tax for Premature Distributions.

Your IRA is intended to provide income for you upon retirement. Accordingly, the
law generally imposes a penalty on premature distributions. If you receive a
taxable distribution from the IRA before reaching age 59 1/2, a nondeductible
10% penalty will be imposed on the portion of the distribution which is included
in your gross income. This penalty is in addition to any income tax you must pay
on the distribution itself. If you receive a distribution from a SIMPLE-IRA
during the first two years after you begin to participate, the penalty tax is
25% rather than 10%. The penalty generally does not apply to the extent that the
distribution is considered a return of nondeductible contributions or a return
of an excess contribution which is permitted tax-free (see below). If you make a
taxable rollover from a Traditional IRA to a Roth IRA and then take a
distribution during the five year period described in the preceding section, the
portion of the distribution that is allocated to the rollover will be subject to
the 10% penalty tax even though it is not otherwise taxable (unless one of the
exceptions to the 10% penalty applies). For purposes of the 10% penalty tax,
distributions from a Roth IRA are treated as made first from contributions other
than rollovers from Traditional IRAs, then from rollovers from Traditional IRAs,
and finally from income. The penalty also will not apply if the distribution is
made due to your permanent disability or death; if the distribution is one of a
series of substantially equal periodic payments made over your life (or life
expectancy) or over the joint lives (or life expectancies) of you and your
beneficiary; or if the total amount of distributions you receive during a year
do not exceed the sum of the following: (1) the amount of tax-deductible medical
expenses you incur during the year (or the amount that you could deduct if you
itemized your deductions); (2) the amount of medical insurance premiums that you
pay after you have been receiving unemployment compensation for at least 12
weeks, provided that you don't receive the distribution after you have been re-
employed for at least 60 days; (3) the amount that you pay for "qualified higher
education expenses" (described in Acorn's separate booklet on Education IRAs)
for you, your spouse, or your children or grandchildren; and (4) "qualified
first time homebuyer expenses." A "qualified first time homebuyer expense" is
any amount that you pay (including settlement, financing and closing expenses)
for the purchase or construction of a principal residence for you, or one of
your or your spouse's children, grandchildren, or ancestors, provided that the
person whose residence is purchased or built (and his or her spouse) has not
owned a principal residence in the past two years. The total amount that you can
treat as qualified first-time homebuyer expenses during your lifetime (either
for purposes of avoiding tax on a distribution from a Roth IRA or avoiding the
10% penalty on a premature distribution) is $10,000. This lifetime $10,000 limit
applies to the person making the IRA withdrawal, not the person who is buying or
building the residence. Finally, the penalty does not apply

                                       8
<PAGE>
 
to the extent that the distribution is rolled over to another IRA or (if
permitted) qualified plan.

Penalty Tax for Excess Contributions.

Contributions to an IRA above the permissible limits are nondeductible and are
subject to an annual nondeductible excise tax of 6% of the amount of such excess
contributions for each year that the excess is not withdrawn or eliminated. The
tax is paid by the person for whose benefit the IRA is established. If the
person who contributed the excess takes no deduction for it and withdraws the
excess amount plus the net earnings attributable to such excess on or before the
due date (including extensions) for filing the federal income tax return for the
year for which the contribution was made, the 6% excise tax will not be applied
but the 10% tax on premature distributions will be applied to the amount of net
earnings.

     Generally, if the excess is withdrawn after the due date (including
extensions) for filing the tax return for the year for which the contribution
was made, not only will the excess contribution be subject to the 6% excise tax,
but the amount of such excess and the net income attributable to it will also be
includible in income; and you will also be subject to the previously mentioned
10% penalty tax on premature distributions if you do not qualify for one of the
exceptions. The law provides, however, that if an individual has made a
contribution (excluding rollover amounts) to an IRA for a year which does not
exceed the maximum deductible limit for the year, all or part of which is an
excess contribution for which he did not claim a deduction, and he does not
correct the excess contribution before the due date (including extensions) for
filing his tax return for the year, he nevertheless may withdraw the excess
amount contributed (without the net income attributable thereto) at any time
without incurring the 10% penalty tax on premature distributions or being
required to include the amount withdrawn in income. The 6% excise tax will be
imposed even in this special situation for the year of the excess contribution
and each subsequent year until the excess is withdrawn or eliminated.

     The rules discussed above generally apply, with some special rules and
exceptions, to Roth IRAs, SEP-IRAs and SIMPLE-IRAs as well as Traditional IRAs.
The law also allows you to withdraw tax-free and without penalty an excess
contribution, regardless of the amount, made with respect to a rollover
contribution (including an attempted rollover contribution), if the excess
contribution occurred because you reasonably relied on erroneous information
required to be supplied by the plan, trust or institution making the
distribution that was the subject of the rollover.

     As an alternative to withdrawing excess contributions made to an IRA, such
amounts may be eliminated by making reduced contributions for subsequent years;
however, you will be required to pay the 6% excise tax on the amount of the
excess for the year of the contribution and for each subsequent year until the
amount of the excess is deducted in a later year for which you have not
contributed the maximum deductible amount. If a contribution is made to your
account in an amount less than the permissible limit in order to correct an
excess contribution for a previous year for which you did not claim a deduction,
you may under certain circumstances, taking into account the limits on
contributions, be allowed to treat the amount of the reduction in the current
year's contribution as an additional contribution for the current taxable year.

Penalty Tax for Under-Distribution.

If after April 1 following the year in which you attain age 70 1/2, the amount
distributed from any type of IRA other than a Roth IRA or Education IRA is less
than the minimum amount required by law to be distributed, a 50% excise tax may
be imposed on any such deficiency. The minimum amount required by law to be
distributed is generally based on your life expectancy or the joint and survivor
life expectancy of you and your beneficiary. However, if your beneficiary is not
your spouse, the law imposes an additional requirement, which is called the
minimum distribution incidental benefit requirement. In general, this
requirement is designed to prevent you from naming a beneficiary who is much
younger than yourself in order to extend your payout period. You should consult
your tax adviser to determine your minimum distribution. This excise tax may
also apply to any type of IRA, including a Roth IRA, if your beneficiary fails
to take the minimum required distri-

                                       9
<PAGE>
 
IRA Disclosure Statement, continued


bution in any year after your death, as described above.

   The Internal Revenue Service may waive the penalty tax for under-distribution
if the deficiency was due to reasonable error and reasonable steps are being
taken to correct the deficiency.

Prohibited Transactions and Pledging Account Assets. If during any taxable year
you engage in a so-called "prohibited transaction" with respect to your IRA, the
account will lose its tax-exempt status. In this event, the fair market value of
all account assets, valued as of the first day of such taxable year, will be
deemed distributed to you and the taxable portion will be includible in your
gross income for the year. The applicable 10% (or 25%) penalty for premature
distributions may also apply if you do not qualify for one of the exceptions.
These prohibited transactions generally include any type of financial
transaction between the IRA and you or your beneficiary, including borrowing or
lending money, buying, selling, or renting property, paying compensation, or a
transaction that indirectly benefits you or your beneficiary personally.
Prohibited transactions may also involve members of your family, companies in
which you have an interest, the sponsoring employer in the case of a SEP-IRA or
SIMPLE-IRA, any person who provides services to the IRA, and certain affiliates
of such persons. However, prohibited transactions involving persons other than
you or your beneficiary result in penalty taxes on the person involved, rather
than disqualification of the IRA. If you pledge your account or any portion
thereof as security for a loan, such pledged portion will be deemed distributed
to you and, to the extent that it does not represent a return of nondeductible
contributions, includible in your gross income. If you have not yet attained age
59 1/2, an additional tax equal to 10% of the amount pledged will be imposed on
such funds includible in gross income. If your spouse engages in a prohibited
transaction with respect to his or her account, the results will be the same.
Any portion of an IRA used to purchase an endowment contract or collectible is
also treated as distributed.

VI. Miscellaneous

Federal Income Tax Withholding. Taxable distributions from an IRA to the covered
individual or to a beneficiary are subject to federal income tax withholding
unless the covered individual or beneficiary elects to have no withholding
apply. The current withholding rate required by the Internal Revenue Code is 10%
for lump sum payments, and regular wage withholding rates for annuities or other
periodic payments. Additional information concerning withholding and election
forms will be available no later than at the time a distribution is requested.

Federal Estate and Gift Taxes. Generally, your IRA will be included in your
estate for federal estate tax purposes. If your spouse is your beneficiary, your
IRA may qualify for a deduction for purposes of that tax. An election under an
IRA to have a distribution payable to a beneficiary on the death of the covered
individual will not be treated as a gift subject to federal gift tax. The amount
that you contribute to an Education IRA for a beneficiary will generally be
treated as a gift to that beneficiary when the contribution is made, and no
additional gift will occur when distributions are paid to the beneficiary.

Reports to the Internal Revenue Service.

As described above, you are required to attach Form 8606 to your return for any
year in which you made nondeductible contributions, or receive distributions
after making nondeductible contributions. You are required to file Form 5329
with the IRS if you owe one of the IRA penalty taxes. These are the taxes on
excess contributions, premature distributions, prohibited transactions and
under-distributions after age 70 1/2, as described above.

Social Security and Self-Employment Taxes. Contributions to a Traditional IRA
are not deductible for purposes of the social security (FICA) and self-
employment taxes. Contributions to a SEP-IRA by your employer are not subject to
social security tax unless you elected to reduce your current compensation to
receive the contributions under a SAR-SEP established prior to 1997. The amount

                                      10
<PAGE>
 
that you elect to defer under a SIMPLE-IRA is subject to social security tax,
but the contributions made by your employer are not.

Financial Information. The growth in value of the mutual fund shares held in
your account can neither be guaranteed nor projected.

Custodian Fees. State Street Bank and Trust Company as the Custodian of your IRA
currently charges an acceptance fee of $5.00 per account, and an annual
maintenance fee of $10.00 per account, per fund in which you have an investment.
An additional $10.00 fee is charged for each disbursement, other than an
automatic installment payout. Note that Spousal IRAs require separate accounts.
Each spouse's account is subject to the above fees.

   If you do not add the $5.00 acceptance fee to your initial contribution, it
will be deducted from your account. The $10.00 annual maintenance fee will be
deducted from your account, unless paid separately when billed in November.

   The Custodian may change any of the above fees from time to time.

IRS Approval Status. Acorn uses prototype Forms 5305-A and 5305-RA, which have
been promulgated and approved by the Internal Revenue Service, for the
establishment of Traditional and Roth IRAs, respectively. The approval of the
IRS relates only to forms used and not to the merits of your account or an
investment in any of the Acorn funds. Further information concerning IRAs can be
obtained from any district office of the IRS.


October 15, 1998

                                      11
<PAGE>
 
Custodial Agreement for a Traditional or SEP-IRA


Form 5305-A
(Revised January 1998)
Department of the Treasury
Internal Revenue Service

Acorn Investment Trust
Custodial Agreement for a Traditional or SEP-IRA
(Under Section 408(a) of the Internal Revenue Code)
(January 1, 1998)

Article I

The Custodian may accept additional cash contributions on behalf of the
Depositor for a tax year of the Depositor. The total cash contributions are
limited to $2,000 for the tax year unless the contribution is a rollover
contribution described in section 402(c), 403(a)(4), 403(b)(8), 408(d)(3), or an
employer contribution to a simplified employee pension plan as described in
section 408(k).

Article II

The Depositor's interest in the balance in the custodial account is
nonforfeitable.

Article III

1. No part of the custodial funds may be invested in life insurance contracts,
nor may the assets of the custodial account be commingled with other property
except in a common trust fund or common investment fund (within the meaning of
section 408(a)(5)).

2. No part of the custodial funds may be invested in collectibles (within the
meaning of section 408(m)) except as otherwise permitted by section 408(m)(3),
which provides an exception for certain gold, silver, and platinum coins, coins
issued under the laws of any state, and certain bullion.

Article IV

1. Notwithstanding any provision of this agreement to the contrary, the
distribution of the Depositor's interest in the custodial account shall be made
in accordance with the following requirements and shall otherwise comply with
section 408(a)(6) and Proposed Regulations section 1.408-8, including the
incidental death benefit provisions of Proposed Regulations section 
1.401(a)(9)-2, the provisions of which are incorporated by reference.

2. Unless otherwise elected by the time distributions are required to begin to
the Depositor under paragraph 3, or to the surviving spouse under paragraph 4,
other than in the case of a life annuity, life expectancies shall be
recalculated annually. Such election shall be irrevocable as to the Depositor
and the surviving spouse and shall apply to all subsequent years. The life
expectancy of a nonspouse beneficiary may not be recalculated.

3. The Depositor's entire interest in the custodial account must be, or begin
to be, distributed by the Depositor's required beginning date, April 1 follow-
ing the calendar year end in which the Depositor reaches age 70 1/2. By that
date, the Depositor may elect, in a manner acceptable to the Custodian, to have
the balance in the custodial account distributed in:

 (a) A single sum payment.

 (b) An annuity contract that provides equal or substantially equal monthly,
 quarterly, or annual payments over the life of the Depositor.

 (c) An annuity contract that provides equal or substantially equal monthly,
 quarterly, or annual payments over the joint and last survivor lives of the
 Depositor and his or her designated beneficiary.

 (d) Equal or substantially equal annual payments over a specified period that
 may not be longer than the Depositor's life expectancy.

 (e) Equal or substantially equal annual payments over a specified period that
 may not be longer than the joint life and last survivor expectancy of the
 Depositor and his or her designated beneficiary.

4. If the Depositor dies before his or her entire interest is distributed to
him or her, the entire remaining interest will be distributed as follows:

 (a) If the Depositor dies on or after distribution of his or her interest has
 begun, distribution must continue to be made in accordance with paragraph 3.

 (b) If the Depositor dies before distribution of his or her interest has begun,
 the entire remaining interest will, at the election of the Depositor or, if the
 Depositor has not

                                      12
<PAGE>
 
 so elected, at the election of the beneficiary or beneficiaries, either

   (i) Be distributed by December 31 of the year containing the fifth
   anniversary of the Depositor's death, or

   (ii) Be distributed in equal or substantially equal payments over the life or
   life expectancy of the designated beneficiary or beneficiaries starting by
   December 31 of the year following the year of the Depositor's death. If,
   however, the beneficiary is the Depositor's surviving spouse, then this
   distribution is not required to begin before December 31 of the year in which
   the Depositor would have reached age 70 1/2.

 (c) Except where distribution in the form of an annuity meeting the
 requirements of section 408(b)(3) and its related regulations has irrevocably
 commenced, distributions are treated as having begun on the Depositor's
 required beginning date, even though payments may actually have been made
 before that date.

 (d) If the Depositor dies before his or her entire interest has been
 distributed and if the beneficiary is other than the surviving spouse, no
 additional cash contributions or rollover contributions may be accepted in the
 account.

5. In the case of a distribution over life expectancy in equal or substantially
equal annual payments, to determine the minimum annual payment for each year,
divide the Depositor's entire interest in the custodial account as of the close
of business on December 31 of the preceding year by the life expectancy of the
Depositor (or the joint life and last survivor expectancy of the Depositor and
the Depositor's designated beneficiary, or the life expectancy of the designated
beneficiary, whichever applies). In the case of distributions under paragraph 3,
determine the initial life expectancy (or joint life and last survivor
expectancy) using the attained ages of the Depositor and designated beneficiary
as of their birthdays in the year the Depositor reaches age 70 1/2. In the case
of a distribution in accordance with paragraph 4(b)(ii), determine life
expectancy using the attained age of the designated beneficiary as of the
beneficiary's birthday in the year distributions are required to commence.

6. The owner of two or more individual retirement accounts may use the
"alternative method" described in Notice 88-38, 1988-1 C.B. 524, to satisfy the
minimum distribution requirements described above. This method permits an
individual to satisfy these requirements by taking from one individual
retirement account the amount required to satisfy the requirement for another.

Article V

1. The Depositor agrees to provide the Custodian with information necessary for
the Custodian to prepare any reports required under section 408(i) and
Regulations section 1.408-5 and 1.408-6.

2. The Custodian agrees to submit reports to the Internal Revenue Service and
the Depositor prescribed by the Internal Revenue Service.

Article VI

Notwithstanding any other articles which may be added or incorporated, the
provisions of Articles I through III and this sentence will be controlling. Any
additional articles that are not consistent with section 408(a) and the related
regulations will be invalid.

Article VII

This agreement will be amended from time to time to comply with the provisions
of the Code and related regulations. Other amendments may be made with the
consent of the persons whose signatures appear below.

Article VIII

1. Form of Contributions.  All contributions and transfers shall be made only
in cash.

2. Investment of Contributions.

 (a) As directed by the Depositor in writing, all contributions shall be used by
 the Custodian to purchase Fund Shares. All income dividends and capital gains
 distributions shall be reinvested in shares of the Fund which declared such
 dividends or distributions unless the Depositor elects in writing, in
 accordance with an opportunity to do so provided by the Fund declaring the
 dividend or distribution, to apply such dividend or distribution to purchase
 other Fund Shares available under this Agreement.

                                      13
<PAGE>
 
Custodial Agreement for a Traditional or SEP-IRA, continued


 (b) A Telephone Exchange Plan ("Exchange Plan"), as described in the
 prospectus(es) of the Funds is available hereunder. After the Custodian
 receives an Exchange Plan authorization deemed by the Custodian to be in proper
 form, the Custodian, upon receipt of telephonic instructions from any person
 representing himself to be the Depositor, may redeem any Fund Shares held by
 the Custodian on behalf of the Depositor and apply the proceeds toward the
 purchase of any other Fund Shares available hereunder, subject to and in
 accordance with the terms and conditions of the Exchange Plan. The Custodian
 shall be entitled to rely and act upon such telephonic instructions, and
 neither the Custodian, the Trust, any other Fund whose shares are available
 hereunder nor their officers, trustees, directors, employees or agents shall be
 liable for any liability, cost or expense for acting on any such instructions.
 In directing any exchange pursuant to the Exchange Plan, the Depositor
 represents that he has obtained a current prospectus of the Fund into which the
 switch is to be made. The Depositor authorizes and directs the Custodian to
 respond to any telephonic inquiries relating to the status of shares owned,
 including but not limited to the number of shares held. The Depositor agrees
 that the authorizations, directions and restrictions contained herein will
 continue until the Custodian receives written notice of any change or
 revocation. The Depositor agrees and understands that the Funds and the
 Custodian reserve the right to refuse any telephonic instructions.

 (c) All Fund Shares acquired by the Custodian shall be registered in the name
 of the Custodian or its nominee.

3. Beneficiaries; Distributions to Minors.

 (a) A Depositor shall have the right by written notice to the Custodian to
 designate one or more beneficiaries to receive any amount to which the
 Depositor may be entitled in the event of his death before the complete
 distribution of his interest, and to change any such beneficiary. Such
 designation or change shall be on the Beneficiary Form provided by the Trust,
 and shall be effective only when filed with the Custodian before the death of
 the Depositor. Such designation may include contingent or successive
 beneficiaries. If no such designation is in effect on a Depositor's death, or
 if no designated beneficiary is living on the date any payment becomes due
 after the Depositor's death, such payment shall be made to the executor or
 administrator of the Depositor's estate. However, if after the Depositor's
 death, his surviving spouse is receiving payments over a specified period, the
 surviving spouse may designate a beneficiary to receive the balance of the
 Custodial Account, if any, on his or her death in accordance with the foregoing
 rules.

 (b) If any person to whom all or a portion of the Depositor's interest is
 payable is a minor, payment of the minor's interest shall be made on behalf of
 the minor to the person designated by the Depositor in the Beneficiary Form to
 receive the minor's interest as Custodian under the Massachusetts Uniform
 Transfers to Minors Act or similar statute. If any person to whom all or a
 portion of the Depositor's interest is payable is a minor and if either the
 Depositor has not so designated a person to receive the minor's interest as
 such Custodian, or the person so designated is unable to act (because of
 incapacity, failing or declining to act, death or otherwise), the Custodian
 shall:

   (i) Distribute the interest to the legal guardian of such minor; or

   (ii) If no guardian has been appointed, designate an adult member of the
   minor's family, a guardian or a trust company (including the Custodian), as
   those terms are defined in the Massachusetts Uniform Transfers to Minors Act
   or similar statute, as custodian for such minor under the Massachusetts
   Uniform Transfers to Minors Act or similar statute and distribute such
   minor's interest to the person so designated. The person designated as
   custodian under the Massachusetts Uniform Transfers to Minors Act or similar
   statute shall hold, manage and distribute such property in accordance with
   the provisions of such statute including, if such statute so requires, a
   total distribution prior to age 21. The distribution of the Depositor's
   interest to the

                                      14
<PAGE>
 
   guardian or the person designated as custodian under the Massachusetts
   Uniform Transfers to Minors Act or similar statute shall be a full discharge
   of the Custodian to the extent of the distribution so made.

 (c) The determination of the Custodian as to the person entitled to receive any
 distribution from the Custodial Account following the death of the Depositor,
 if made in good faith, shall be conclusive and binding on all persons claiming
 an interest in the Custodial Account; provided that nothing provided herein
 shall be construed to preclude the Custodian from filing an action in the
 nature of interpleader or other appropriate proceeding in a court of competent
 jurisdiction to determine the person entitled to receive such distribution. Any
 expenses incurred by the Custodian in determining the person entitled to
 receive a distribution from the Custodial Account, including without limitation
 attorneys fees in any such action, shall be reimbursed from the Custodial
 Account.

4. Inalienability of Benefits. The benefits provided hereunder shall not be
subject to alienation, assignment, garnishment, attachment, execution or levy of
any kind of any attempt to cause such benefits to be so subjected shall not be
recognized except to the extent as may be required by law.

5. Distributions to Surviving Spouse. If distributions from the Custodial
Account are to be made to the Depositor's surviving spouse, or to a trust of
which the Depositor's surviving spouse is the income beneficiary, the amount
which the surviving spouse (or such trust) is entitled to receive in each year
shall not be less than the income of the Custodial Account (or of the portion of
the Custodial Account with respect to which the surviving spouse or such trust
is the beneficiary) for such year, as determined under section 2056(b)(7) of the
Code.

6. Minimum Distributions; Election not to Recalculate Life Expectancies. The
following provisions supplement the provisions of Article IV with respect to
minimum required distributions, and shall control over the provisions of Article
IV in the event of any inconsistency. All paragraph references in this paragraph
6 are to paragraphs of Article IV unless otherwise provided.

 (a) If the Depositor fails to withdraw the entire balance in the Custodial
 Account by the April 1 of the year following the year in which he attains age
 70 1/2, he shall be deemed to have elected to receive payments under paragraph
 3(d) or, if he has a designated beneficiary (as determined under Part D of
 Proposed Regulations section 1.401(a)(9)-1) under paragraph 3(e). A beneficiary
 shall be deemed to have elected the method described in paragraph 4(b)(ii) if
 either he withdraws the minimum amount required for the first year under the
 method described in paragraph 4(b)(ii) and does not specifically elect the
 method described in paragraph 4(b)(i) by the end of such year, or if the date
 specified in paragraph 4(b)(i) occurs first and he has not withdrawn the entire
 balance in the Custodial Account by that time; otherwise, the beneficiary shall
 be deemed to have elected the method described in paragraph 4(b)(i).

 (b) If there is more than one beneficiary entitled to receive distributions on
 equal priority upon the death of the Depositor or a prior beneficiary then, to
 the extent permitted by Proposed Regulations section 1.401(a)(9)-1, Q&A H-2,
 and subject to such requirements and limitations as the Custodian may
 establish, the Custodial Account may be divided into separate accounts for
 purposes of Article IV and this paragraph. Whenever distributions after the
 death of the Depositor are to be made to the Depositor's surviving spouse and
 to one or more beneficiaries other than the surviving spouse, and any provision
 of Article IV, this paragraph 6, or the minimum distribution requirements
 provides different treatment for the portion of the Custodial Account to be
 distributed to the surviving spouse, then such portion, and the income earned
 thereon, shall be separated and treated as a separate Custodial Account with
 respect to such surviving spouse.

 (c) Notwithstanding the references to "equal or substantially equal" payments,
 if the Depositor or a beneficiary is receiving distributions under paragraph
 3(d), 3(e), or 4(b)(ii), he may withdraw amounts that exceed the minimum amount
 required by paragraph 5 in any year,

                                      15
<PAGE>
 
Custodial Agreement for a Traditional or SEP-IRA, continued


 provided that any excess shall not be credited against the minimum amount
 required to be withdrawn in subsequent years. Withdrawals may also be made at
 irregular intervals, provided that the minimum amount required for each year
 shall be withdrawn by the last day of such year, except that the minimum amount
 for the year in which the Depositor attains age 70 1/2, but no subsequent year,
 may be withdrawn by April 1 of the following year.

 (d) In lieu of the methods of recalculating life expectancies annually as
 specified in paragraph 2, the Depositor may elect for purposes of paragraph
 3(d) or 3(e), and the Depositor's surviving spouse may elect for purposes of
 paragraph 4(b)(ii), to have his life expectancy, or his and his designated
 beneficiary's joint and last survivor life expectancy, or the surviving
 spouse's life expectancy, initially calculated in the year specified in
 paragraph 5 and thereafter reduced by one year in each subsequent year. All
 elections described in this paragraph 6(d) shall be made in writing in
 accordance with procedures established by the Custodian and the Proposed
 Regulations or successors thereto. Such elections must be made and, if made,
 shall be irrevocable after the date upon which distributions are required to
 commence under paragraph 3 or 4(b)(ii).

 (e) All references to the Proposed Regulations section 1.401(a)(9)-1 and
 1.401(a)(9)-2 contained in Article IV and this paragraph 6 include the
 applicable provisions of Proposed Regulations section 1.408-8 applying such
 Proposed Regulations to individual retirement accounts, any subsequent
 amendments to any such Proposed Regulations, and the applicable provisions of
 the permanent Regulations, when issued, all of which are incorporated by
 reference and shall control over any contrary provision of this Agreement.
 Reference to specific provisions of the Proposed Regulations shall not be
 construed to limit reference to other provisions where appropriate in the
 interpretation of Article IV and this paragraph 6.

 (f) For all purposes of Article IV and this paragraph 6, life expectancy and
 joint-life and last-survivor expectancy are calculated based on information
 provided by the Depositor (or the Depositor's authorized agent, beneficiary,
 executor, or administrator) using the expected return multiples under Treasury
 Regulations Section 1.72-9. The Custodian will not be liable for errors in such
 calculations resulting Form its reliance on such information.

 (g) Notwithstanding anything herein to the contrary, all distributions shall be
 made by the Custodian in such manner and in such amounts as may be specified in
 written instructions received from time to time by the Depositor or the
 beneficiary, as the case may be and all such instructions shall be deemed to
 constitute a certification by the Depositor or beneficiary that the
 distribution so directed is one that the Depositor or beneficiary is permitted
 to receive. In addition, the Custodian shall have no liability with respect to
 any distribution from the Account in accordance with the directions of the
 Depositor or beneficiary or the failure to make a distribution in the absence
 of such instructions or any consequences thereof including, but not limited to,
 excise and other taxes and penalties which might accrue or be assessed, nor
 shall the Custodian be under any duty to make any inquiry or investigation with
 respect thereto. If any assets held on the Depositor's behalf in a Custodial
 Account are transferred directly to a trustee or Custodian of another
 individual retirement account described in Code Section 408(a) established for
 the Depositor, it shall be the Depositor's responsibility to ensure that any
 requested minimum distribution required by Article IV is made prior to giving
 the Custodian such transfer instructions.

 (h) Any annuity contract purchased for the Depositor pursuant to this Agreement
 shall be immediately distributed to the Depositor, and the custodial
 relationship shall terminate upon such distribution.

7. Administration.

 (a) Except as otherwise provided in this Agreement, the Custodian shall, as
 directed in writing, on behalf of the Depositor:

   (i) Receive contributions pursuant to the provisions

                                      16
<PAGE>
 
   of the Agreement;

   (ii) Hold, invest and reinvest the contributions in Fund Shares;

   (iii) Register any property in the Custodial Account in the name of the
   Custodian or its nominee; and

   (iv) Make distributions from the Custodial Account in cash or in Fund Shares
   pursuant to the provisions of this Agreement.

 (b) In addition to the provisions of Article V, the Custodian shall deliver or
 cause to be executed and delivered to the Depositor all notices, prospectuses,
 financial statements, proxies and proxy soliciting material relating to assets
 credited to the custodial account. No Fund Shares shall be voted, and no other
 action shall be taken pursuant to such documents, except upon receipt of
 adequate written instructions from the Depositor.

 (c) The Custodian shall keep accurate and detailed account of its receipts,
 investments and disbursements. As soon as practicable after the end of each
 calendar year, and whenever required by regulations adopted under the Act or
 the Code, the Custodian shall file with the Depositor a written report of the
 Custodian's transactions relating to the Custodial Account during the period
 from the last previous accounting, and shall file such other reports with the
 Internal Revenue Service as may be required of the Custodian by regulation.

 (d) Unless the Depositor sends the Custodian written objection to a report
 within 60 days after its receipt, the Depositor shall be deemed to have
 approved such report, and in such case the Custodian shall be forever released
 and discharged with respect to all matters and things included therein. The
 Custodian may seek a judicial settlement of its accounts. In any such
 proceeding the only necessary party thereto in addition to the Custodian shall
 be the Depositor unless otherwise required by law.

 (e) The Custodian shall have no duties whatsoever except such duties as are
 specifically provided for herein, and no implied covenant or obligation shall
 be read into this Agreement against the Custodian. The Custodian shall not be
 liable for a mistake in judgment, for any action taken, or any failure to act,
 in good faith, or for any loss that is not a result of its gross negligence,
 except as expressly required by the Act and regulations promulgated thereunder.
 In performing its duties under this Agreement, the Custodian may hire agents,
 experts and attorneys and may delegate discretionary powers to, and rely upon
 information and advice furnished by, such agents, experts and attorneys.

 (f) The Depositor agrees to indemnify and hold the Custodian harmless from and
 against any liability that the Custodian may incur in the administration of the
 Custodial Account, unless arising from the Custodian's own gross negligence or
 willful misconduct.

 (g) The Custodian shall be under no duty to question any direction of the
 Depositor with respect to the investment of contributions, or to make
 suggestions to the Depositor with respect to the investment, retention or
 disposition of any contributions or assets held in the Custodial Account.

 (h) The Custodian shall pay out of the Custodial Account expenses of
 administration, including the fees of counsel employed by the Custodian, taxes,
 if any, and its fees for maintaining the Custodial Account, which are set forth
 in the Disclosure Statement but may be revised from time to time by the
 Custodian and the Trust. The Custodian may sell Fund Shares and use the
 proceeds of sale to pay the foregoing fees and expenses.

 (i) The Custodian may resign as Custodian of any Depositor's Custodial Account
 or as Custodian of all accounts adopted under the provisions of this Plan, in
 either case upon 30 days' prior notice to the Trust and 30 days' prior notice
 to each Depositor who will be affected by such resignation. If the Trust or the
 Depositor does not appoint a successor Custodian within 30 days after the
 mailing of such notice, the Custodian will terminate the Custodial Account.

 (j) The Depositor shall be solely and fully responsible for all taxes and
 penalties which might accrue or be assessed with respect to any excess
 contributions, premature distributions or distributions which are below

                                      17
<PAGE>
 
Custodial Agreement for a Traditional or SEP-IRA, continued


 the annual minimum distribution required.

 (k) The Custodian shall be entitled to receive and may charge against the
 Director's Custodial Account such reasonable compensation for its services in
 accordance with its fee schedule as from time to time in effect, and shall also
 be entitled to reimbursement of its expenses as Custodian under this Agreement.
 The Custodian will notify the Depositor in writing of any change in its fee
 schedule.

 (l) This Agreement and the Custodial Account created hereby shall be subject to
 the applicable laws, rules and regulations, as the same may from time to time
 be amended, of the Federal government and the Commonwealth of Massachusetts and
 the agencies and instrumentalities of each having jurisdiction thereof, and
 shall be governed by and construed, administered and enforced according to the
 law of the Commonwealth of Massachusetts. All contributions to the Custodial
 Account shall be deemed to take place in the Commonwealth of Massachusetts.

 (m) The Custodian and Depositor hereby waive and agree to waive right to trial
 by jury in an action or proceeding instituted in respect to this Custodial
 Account. The Depositor further agrees that the venue of any litigation between
 him and the Custodian with respect to the Custodial Account shall be in the
 County of Suffolk, Commonwealth of Massachusetts.

 (n) All communications or notices required or permitted to be given herein
 shall be deemed to be given upon receipt by the Custodian at P. O. Box 8502,
 Boston, MA 02266-8502, by the Trust at 227 W. Monroe St., Suite 3000, Chicago,
 IL, 60606, or the Depositor at his most recent address shown in the Custodian's
 records. The Depositor agrees to advise the Custodian promptly, in writing, of
 any change of address.

 (o) Subject to the last paragraph of this subparagraph (o), the Depositor may
 revoke the Custodial Account established hereunder by mailing or delivering a
 written notice of revocation to the Custodian within seven days after the
 Depositor first receives the Disclosure Statement related to the Custodial
 Account. Mailed notice is treated as given to the Custodian on the date of the
 postmark (or on the date of Post Office certification or registration in the
 case of notice sent by certified or registered mail). Upon timely revocation,
 the Depositor will receive a payment equal to the initial contribution, without
 adjustment for administrative expenses, commissions or sales charges,
 fluctuations in market value or other changes. The Depositor may certify in the
 Application that the Depositor received the Disclosure Statement related to the
 Custodial Account at least seven days before signing the Application to
 establish the Custodial Account, and the Custodian may rely on such
 certification.

 (p) The Depositor may in writing appoint an investment advisor with respect to
 the Custodial Account on a form acceptable to the Custodian and the Trust. The
 investment advisor's appointment will be in effect until written notice to the
 contrary is received by the Custodian and the Trust. While an investment
 advisor's appointment is in effect, the investment advisor may issue investment
 directions or may issue orders for the sale or purchase of shares of one or
 more Funds to the Trust, and the Trust and its agents will be fully protected
 in carrying out such investment directions or orders to the same extent as if
 they had been given by the Depositor. The Depositor's appointment of any
 investment advisor will also be deemed to be instructions to the Custodian and
 the Trust to pay such investment advisor's fees to the investment advisor from
 the Custodial Account hereunder without additional authorization by the
 Depositor or the Custodian.

8. The Trust

 (a) The Depositor delegates to the Trust the power with respect to this
 Agreement: (i) to remove the Custodian and select a successor Custodian; and
 (ii) to amend this Agreement as provided in paragraph 9.

 (b) The powers herein delegated to the Trust shall be exercised by such officer
 thereof as the Trust may designate from time to time, and shall be exercised
 only when similarly exercised with respect to all other Depositors establishing
 IRA accounts.

 (c) Neither the Trust nor any officer, director, trustee,

                                      18
<PAGE>
 
 board, committee, employee or member of the Trust shall incur any liability of
 any nature to the Depositor or beneficiary or other person in connection with
 any act done or omitted to be done in good faith in the exercise of any power
 or authority herein delegated to the Trust.

 (d) If the Trust shall hereafter determine that it is no longer desirable for
 the Trust to continue to exercise any of the powers hereby delegated to the
 Trust, it may relieve itself of any further responsibilities hereunder by
 notice in writing to the Depositor and the Custodian at least 60 days before
 the date on which the Trust proposes to discontinue the exercise of the powers
 delegated to it.

9. Amendment and Termination.

 (a) The Depositor delegates to the Trust the power to amend this Agreement
 (including retroactive amendment). A copy of any such amendment shall be
 furnished to the Custodian, and no such amendment shall have the effect of
 increasing the duties or obligations of the Custodian until it has been
 approved by the Custodian. A copy of any such amendment shall also be furnished
 to the Depositor, but no delay in furnishing such copy shall affect the
 effectiveness of such amendment.

 (b) The Depositor may amend his/her Application (including retroactive
 amendment) by submitting to the Custodian (i) a copy of such amended
 Application, and (ii) evidence satisfactory to the Custodian that the Agreement
 as amended by such amended Application will continue to qualify as an
 Individual Retirement Account under the provisions of section 408(a) of the
 Code.

 (c) No amendment shall be effective if it would cause or permit (i) any part of
 the Custodial Account to be diverted to any purpose that is not for the
 exclusive benefit of the Depositor and his beneficiaries; (ii) the Depositor to
 be deprived of any portion of his interest in the Custodial Account, unless
 such action is taken in order to satisfy qualification requirements under the
 Code; or (iii) the imposition of an additional duty on the Custodian without
 its written consent.

 (d) The Depositor reserves the right to terminate his adoption of this
 Agreement by instrument in writing signed by him and filed with the Custodian.

 (e) In the event that the assets of any investment company (including any
 series of the Trust) in which the Custodial Account is invested are transferred
 to or acquired by any other investment company or other commingled investment
 fund which is a permissible investment for an individual retirement account, by
 merger or otherwise, the Trust may make such amendments to this Agreement, or
 take such other action, as it may determined to be necessary or appropriate to
 accomplish such transaction and the exchange of Fund Shares for shares or other
 appropriate units of ownership in such successor fund. The consent of the
 Depositor shall not be required for any such amendment or action, but the
 Depositor shall be promptly notified thereof, and shall have the right to
 withdraw the funds in the Custodial Account without fee, charge, load or
 penalty of any kind.

10. Definitions.

Whenever used in this Agreement, the following terms shall have the meanings set
forth below unless otherwise expressly provided herein:

 (a) Act. The Employee Retirement Income Security Act of 1974, as amended from
 time to time.

 (b) Agreement. This Custodial Agreement for a Regular or SEP-IRA Account,
 including the Application, as amended from time to time.

 (c) Application. The IRA Application Form, constituting an agreement between
 the Depositor and the Custodian, by which the Depositor adopts this Agreement

 (d) Code. The Internal Revenue Code of 1986, as amended from time to time.
 Reference to a section of the Code shall include that section and any
 comparable section or sections of any future legislation that amends,
 supplements or supersedes that section.

 (e) Custodial Account. The account established for the Depositor pursuant to
 this Agreement.

 (f) Custodian. The bank named in the Application.

 (g) Depositor. The individual who adopts this Agreement as provided therein.

 (h) Fund Shares. Shares issued by the Trust or shares of any other regulated
 investment company for which the

                                      19
<PAGE>
 
Custodial Agreement for a Traditional or SEP-IRA, continued


 Custodian acts as transfer agent and which may be available hereunder from time
 to time pursuant to an agreement between the Custodian and the Trust. No Fund
 shall be available for investment under this Agreement (i) before the date the
 prospectus for that Fund discloses its availability, (ii) with respect to any
 Depositor who resides in any state or other jurisdiction in which shares of the
 Fund are not available for sale, or (iii) with respect to any Depositor not
 eligible to purchase Fund shares directly, when sales of Fund shares are
 restricted.

 (i) Trust. Acorn Investment Trust, a regulated investment company.

11. Conflict in Provisions. To the extent that any of the provisions of Article
VIII shall conflict with the provisions of Articles IV, V, or VII, the
provisions of Article VIII shall prevail.

12. Loss of Exemption. If the Custodian receives notice that the Custodial
Account has lost its tax-exempt status under section 408(a) of the Code for any
reason, including by reason of a transaction prohibited by section 4975 of the
Code, the Custodian shall distribute to the Depositor the entire balance in the
Account, in cash or in kind, in the sole discretion of the Custodian no later
than 90 days after the date the Custodian receives such notice.

                                      20
<PAGE>
 
Custodial Agreement for a Roth IRA


Form 5305-RA
(January 1998)
Department of the Treasury
Internal Revenue Service

Acorn Investment Trust
Custodial Agreement for a Roth IRA
(Under Section 408A of the Internal Revenue Code)
(January 1, 1998)

Article I

1. If this Roth IRA is not designated as a Roth Conversion IRA, then, except in
the case of a rollover contribution described in section 408A(e), the Custodian
will accept only cash contributions and only up to a maximum amount of $2,000
for any tax year of the Depositor.

2. If this Roth IRA is designated as a Roth Conversion IRA, no contributions
other than IRA Conversion Contributions made during the same tax year will be
accepted.

Article II

The $2,000 limit described in Article I is gradually reduced to $0 between
certain levels of adjusted gross income (AGI). For a single Depositor, the
$2,000 annual contribution is phased out between AGI of $95,000 and $110,000;
for a married Depositor who files jointly, between AGI of $150,000 and $160,000;
and for a married Depositor who files separately, between $0 and $10,000. In the
case of a conversion, the Custodian will not accept IRA Conversion Contributions
in a tax year if the Depositor's AGI for that tax year exceeds $100,000 or if
the Depositor is married and files a separate return. Adjusted gross income is
defined in section 408A(c)(3) and does not include IRA Conversion Contributions.

Article III

The Depositor's interest in the balance in the custodial account is
nonforfeitable.

Article IV

1. No part of the custodial funds may be invested in life insurance contracts,
nor may the assets of the custodial account be commingled with other property
except in a common trust fund or common investment fund (within the meaning of
section 408(a)(5)).

2. No part of the custodial funds may be invested in collectibles (within the
meaning of section 408(m)) except as otherwise permitted by section 408(m)(3),
which provides an exception for certain gold, silver, and platinum coins, coins
issued under the laws of any state, and certain bullion.

Article V

1. If the Depositor dies before his or her entire interest is distributed to
him or her and the grantor's surviving spouse is not the sole beneficiary, the
entire remaining interest will, at the election of the Depositor or, if the
Depositor has not so elected, at the election of the beneficiary or
beneficiaries, either:

 (a) Be distributed by the December 31 of the year containing the fifth
 anniversary of the Depositor's death, or

 (b) Be distributed over the life expectancy of the designated beneficiary
 starting no later than December 31 of the year following the year of the
 Depositor's death. If distributions do not begin by the death described in (b),
 distribution method (a) will apply.

2. In the case of a distribution method 1.(b) above, to determine the minimum
annual payment for each year, divide the grantor's entire interest in the trust
as of the close of business on December 31 of the preceding year by the life
expectancy of the designated beneficiary using the attained age of the
designated beneficiary as of the beneficiary's birthday in the year
distributions are required to commence and subtract 1 for each subsequent year.

3. If the Depositor's spouse is the sole beneficiary on the Depositor's date of
death, such spouse will then be treated as the Depositor.

Article VI

1. The Depositor agrees to provide the Custodian with information necessary for
the Custodian to prepare any reports required under sections 408(i) and
408A(d)(3)(E), and Regulations sections 1.408-5 and 1.408-6, and under guidance
published by the Internal Revenue Service.

                                      21
<PAGE>
 
Custodial Agreement for a Roth IRA, continued


2. The Custodian agrees to submit reports to the Internal Revenue Service and
the Depositor prescribed by the Internal Revenue Service.

Article VII

Notwithstanding any other articles which may be added or incorporated, the
provisions of Articles I through IV and this sentence will be controlling. Any
additional articles that are not consistent with section 408A, the related
regulations, and other published guidance will be invalid.

Article VIII

This agreement will be amended from time to time to comply with the provisions
of the Code, related regulations, and other published guidance. Other amendments
may be made with the consent of the persons whose signatures appear below.

Article IX

1. Form of Contributions. Except as provided in Paragraph 2 of Article I, all
contributions and transfers shall be made only in cash.

2. Investment of Contributions.

 (a) As directed by the Depositor in writing, all contributions shall be used by
 the Custodian to purchase Fund Shares. All income dividends and capital gains
 distributions shall be reinvested in shares of the Fund which declared such
 dividends or distributions unless the Depositor elects in writing, in
 accordance with an opportunity to do so provided by the Fund declaring the
 dividend or distribution, to apply such dividend or distribution to purchase
 other Fund Shares available under this Agreement.

 (b) A Telephone Exchange Plan ("Exchange Plan"), as described in the
 prospectus(es) of the Funds is available hereunder. After the Custodian
 receives an Exchange Plan authorization deemed by the Custodian to be in proper
 form, the Custodian, upon receipt of telephonic instructions from any person
 representing himself to be the Depositor, may redeem any Fund Shares held by
 the Custodian on behalf of the Depositor and apply the proceeds toward the
 purchase of any other Fund Shares available hereunder, subject to and in
 accordance with the terms and conditions of the Exchange Plan. The Custodian
 shall be entitled to rely and act upon such telephonic instructions, and
 neither the Custodian, the Trust, any other Fund whose shares are available
 hereunder nor their officers, trustees, directors, employees or agents shall be
 liable for any liability, cost or expense for acting on any such instructions.
 In directing any exchange pursuant to the Exchange Plan, the Depositor
 represents that he has obtained a current prospectus of the Fund into which the
 switch is to be made. The Depositor authorizes and directs the Custodian to
 respond to any telephonic inquiries relating to the status of shares owned,
 including but not limited to the number of shares held. The Depositor agrees
 that the authorizations, directions and restrictions contained herein will
 continue until the Custodian receives written notice of any change or
 revocation. The Depositor agrees and understands that the Funds and the
 Custodian reserve the right to refuse any telephonic instructions.

 (c) All Fund Shares acquired by the Custodian shall be registered in the name
 of the Custodian or its nominee.

3. Beneficiaries; Distributions to Minors.

 (a) A Depositor shall have the right by written notice to the Custodian to
 designate one or more beneficiaries to receive any amount to which the
 Depositor may be entitled in the event of his death before the complete
 distribution of his interest, and to change any such beneficiary. Such
 designation or change shall be on the Beneficiary Form provided by the Trust,
 and shall be effective only when filed with the Custodian before the death of
 the Depositor. Such designation may include contingent or successive
 beneficiaries. If no such designation is in effect on a Depositor's death, or
 if no designated beneficiary is living on the date any payment becomes due
 after the Depositor's death, such payment shall be made to the executor or
 administrator of the Depositor's estate. However, if after the Depositor's
 death, his surviving spouse is receiving pay-

                                      22
<PAGE>
 
 ments over a specified period, the surviving spouse may designate a beneficiary
 to receive the balance of the Custodial Account, if any, on his or her death in
 accordance with the foregoing rules.

 (b) If any person to whom all or a portion of the Depositor's interest is
 payable is a minor, payment of the minor's interest shall be made on behalf of
 the minor to the person designated by the Depositor in the Beneficiary Form to
 receive the minor's interest as Custodian under the Massachusetts Uniform
 Transfers to Minors Act or similar statute. If any person to whom all or a
 portion of the Depositor's interest is payable is a minor and if either the
 Depositor has not so designated a person to receive the minor's interest as
 such Custodian, or the person so designated is unable to act (because of
 incapacity, failing or declining to act, death or otherwise), the Custodian
 shall:

   (i) Distribute the interest to the legal guardian of such minor; or

   (ii) If no guardian has been appointed, designate an adult member of the
   minor's family, a guardian or a trust company (including the Custodian), as
   those terms are defined in the Massachusetts Uniform Transfers to Minors Act
   or similar statute, as custodian for such minor under the Massachusetts
   Uniform Transfers to Minors Act or similar statute and distribute such
   minor's interest to the person so designated. The person designated as
   custodian under the Massachusetts Uniform Transfers to Minors Act or similar
   statute shall hold, manage and distribute such property in accordance with
   the provisions of such statute including, if such statute so requires, a
   total distribution prior to age 21. The distribution of the Depositor's
   interest to the guardian or the person designated as custodian under the
   Massachusetts Uniform Transfers to Minors Act or similar statute shall be a
   full discharge of the Custodian to the extent of the distribution so made.

 (c) The determination of the Custodian as to the person entitled to receive any
 distribution from the Custodial Account following the death of the Depositor,
 if made in good faith, shall be conclusive and binding on all persons claiming
 an interest in the Custodial Account; provided that nothing provided herein
 shall be construed to preclude the Custodian from filing an action in the
 nature of interpleader or other appropriate proceeding in a court of competent
 jurisdiction to determine the person entitled to receive such distribution. Any
 expenses incurred by the Custodian in determining the person entitled to
 receive a distribution from the Custodial Account, including without limitation
 attorneys fees in any such action, shall be reimbursed from the Custodial
 Account.

4. Inalienability of Benefits. The benefits provided hereunder shall not be
subject to alienation, assignment, garnishment, attachment, execution or levy of
any kind of any attempt to cause such benefits to be so subjected shall not be
recognized except to the extent as may be required by law.

5. Distributions to Surviving Spouse. If distributions from the Custodial
Account are to be made to the Depositor's surviving spouse, or to a trust of
which the Depositor's surviving spouse is the income beneficiary, the amount
which the surviving spouse (or such trust) is entitled to receive in each year
shall not be less than the income of the Custodial Account (or of the portion of
the Custodial Account with respect to which the surviving spouse or such trust
is the beneficiary) for such year, as determined under section 2056(b)(7) of the
Code.

6. Minimum Distributions; Election not to Recalculate Life Expectancies. The
following provisions supplement the provisions of Article V with respect to
minimum required distributions to a beneficiary following the death of the
Depositor, and shall control over the provisions of Article V in the event of
any inconsistency. All paragraph references in this paragraph 6 are to
paragraphs of Article V unless otherwise provided.

 (a) A beneficiary shall be deemed to have elected the method described in
 paragraph 1(b) if either he withdraws the minimum amount required for the first
 year under the method described in paragraph 1(b) and does

                                      23
<PAGE>
 
Custodial Agreement for a Roth IRA, continued


 not specifically elect the method described in paragraph 1(a) by the end of
 such year, or if the date specified in paragraph 1(a) occurs first and he has
 not withdrawn the entire balance in the Custodial Account by that time;
 otherwise, the beneficiary shall be deemed to have elected the method described
 in paragraph 1(a).

 (b) If there is more than one beneficiary entitled to receive distributions on
 equal priority upon the death of the Depositor or a prior beneficiary then, to
 the extent permitted by Proposed Regulations section 1.401(a)(9)-1, Q&A H-2,
 and subject to such requirements and limitations as the Custodian may
 establish, the Custodial Account may be divided into separate accounts for
 purposes of Article V and this paragraph.

 (c) Notwithstanding the references to "equal or substantially equal" payments,
 if a beneficiary is receiving distributions under paragraph 1(b), he may
 withdraw amounts that exceed the minimum amount required by paragraph 2 in any
 year, provided that any excess shall not be credited against the minimum amount
 required to be withdrawn in subsequent years. Withdrawals may also be made at
 irregular intervals, provided that the minimum amount required for each year
 shall be withdrawn by the last day of such year.

 (d) Notwithstanding paragraph (3), a surviving spouse of a deceased Depositor
 may elect not to be treated as the Depositor, but instead to be subject to
 paragraph (1), in which event the required starting date for the method
 provided in paragraph 1(b) shall be the later of the date specified therein or
 December 31 of the year in which the Depositor would have attained the age of
 70 1/2. In addition, a surviving spouse may, in lieu of the method specified in
 paragraph 2, elect to have his or her life expectancy determined each year on
 the basis of his or her age attained in such year. All elections described in
 this paragraph 6(d) shall be made in writing referring explicitly to this
 paragraph 6(d) and in accordance with procedures established by the Custodian
 and the Proposed Regulations or successors thereto. Such elections must be made
 and, if made, shall be irrevocable after the date upon which distributions are
 required to commence under paragraph 1.

 (e) All references to the Proposed Regulations section 1.401(a)(9)-1 contained
 in Article V and this paragraph 6 include the applicable provisions of Proposed
 Regulations section 1.408-8 applying such Proposed Regulations to individual
 retirement accounts, any subsequent amendments to any such Proposed
 Regulations, and the applicable provisions of the permanent Regulations, when
 issued, all of which are incorporated by reference and shall control over any
 contrary provision of this Agreement. Reference to specific provisions of the
 Proposed Regulations shall not be construed to limit reference to other
 provisions where appropriate in the interpretation of Article V and this
 paragraph 6.

 (f) For all purposes of Article IV and this paragraph 6, life expectancy and
 joint-life and last-survivor expectancy are calculated based on information
 provided by the Depositor (or the Depositor's authorized agent, beneficiary,
 executor, or administrator) using the expected return multiples under Treasury
 Regulations Section 1.72-9. The Custodian will not be liable for errors in such
 calculations resulting Form its reliance on such information.

 (g) Notwithstanding anything herein to the contrary, all distributions shall be
 made by the Custodian in such manner and in such amounts as may be specified in
 written instructions received from time to time by the Depositor or the
 beneficiary, as the case may be and all such instructions shall be deemed to
 constitute a certification by the Depositor or beneficiary that the
 distribution so directed is one that the Depositor or beneficiary is permitted
 to receive. In addition, the Custodian shall have no liability with respect to
 any distribution from the Account in accordance with the directions of the
 Depositor or beneficiary or the failure to make a distribution in the absence
 of such instructions or any consequences thereof including, but not limited to,
 excise and other taxes and penalties which

                                      24
<PAGE>
 
 might accrue or be assessed, nor shall the Custodian be under any duty to make
 any inquiry or investigation with respect thereto.

 (h) Any annuity contract purchased for the Depositor pursuant to this Agreement
 shall be immediately distributed to the Depositor, and the custodial
 relationship shall terminate upon such distribution.

7.  Administration.

 (a) Except as otherwise provided in this Agreement, the Custodian shall, as
 directed in writing, on behalf of the Depositor:

   (i) Receive contributions pursuant to the provisions of the Agreement;

   (ii) Hold, invest and reinvest the contributions in Fund Shares;

   (iii) Register any property in the Custodial Account in the name of the
   Custodian or its nominee; and

   (iv) Make distributions from the Custodial Account in cash or in Fund Shares
   pursuant to the provisions of this Agreement.

 (b) In addition to the provisions of Article VI, the Custodian shall deliver or
 cause to be executed and delivered to the Depositor all notices, prospectuses,
 financial statements, proxies and proxy soliciting material relating to assets
 credited to the custodial account. No Fund Shares shall be voted, and no other
 action shall be taken pursuant to such documents, except upon receipt of
 adequate written instructions from the Depositor.

 (c) The Custodian shall keep accurate and detailed account of its receipts,
 investments and disbursements. As soon as practicable after the end of each
 calendar year, and whenever required by regulations adopted under the Act or
 the Code, the Custodian shall file with the Depositor a written report of the
 Custodian's transactions relating to the Custodial Account during the period
 from the last previous accounting, and shall file such other reports with the
 Internal Revenue Service as may be required of the Custodian by regulation.

 (d) Unless the Depositor sends the Custodian written objection to a report
 within 60 days after its receipt, the Depositor shall be deemed to have
 approved such report, and in such case the Custodian shall be forever released
 and discharged with respect to all matters and things included therein. The
 Custodian may seek a judicial settlement of its accounts. In any such
 proceeding the only necessary party thereto in addition to the Custodian shall
 be the Depositor unless otherwise required by law.

 (e) The Custodian shall have no duties whatsoever except such duties as are
 specifically provided for herein, and no implied covenant or obligation shall
 be read into this Agreement against the Custodian. The Custodian shall not be
 liable for a mistake in judgment, for any action taken, or any failure to act,
 in good faith, or for any loss that is not a result of its gross negligence,
 except as expressly required by the Act and regulations promulgated thereunder.
 In performing its duties under this Agreement, the Custodian may hire agents,
 experts and attorneys and may delegate discretionary powers to, and rely upon
 information and advice furnished by, such agents, experts and attorneys.

 (f) The Depositor agrees to indemnify and hold the Custodian harmless from and
 against any liability that the Custodian may incur in the administration of the
 Custodial Account, unless arising from the Custodian's own gross negligence or
 willful misconduct.

 (g) The Custodian shall be under no duty to question any direction of the
 Depositor with respect to the investment of contributions, or to make
 suggestions to the Depositor with respect to the investment, retention or
 disposition of any contributions or assets held in the Custodial Account.

 (h) The Custodian shall pay out of the Custodial Account expenses of
 administration, including the fees of counsel employed by the Custodian, taxes,
 if any, and its fees for maintaining the Custodial Account, which are set forth
 in the Disclosure Statement but may be revised from time to time by the
 Custodian and the Trust. The Custodian may sell Fund Shares and use the
 proceeds of sale to pay the foregoing fees and expenses.

                                      25
<PAGE>
 
Custodial Agreement for a Roth IRA, continued


 (i) The Custodian may resign as Custodian of any Depositor's Custodial Account
 or as Custodian of all accounts adopted under the provisions of this Plan, in
 either case upon 30 days' prior notice to the Trust and 30 days' prior notice
 to each Depositor who will be affected by such resignation. If the Trust or the
 Depositor does not appoint a successor Custodian within 30 days after the
 mailing of such notice, the Custodian will terminate the Custodial Account.

 (j) The Depositor shall be solely and fully responsible for all taxes and
 penalties which might accrue or be assessed with respect to any excess
 contributions, premature distributions or distributions which are below the
 annual minimum distribution required.

 (k) The Custodian shall be entitled to receive and may charge against the
 Depositor's Custodial Account such reasonable compensation for its services in
 accordance with its fee schedule as from time to time in effect, and shall also
 be entitled to reimbursement of its expenses as Custodian under this Agreement.
 The Custodian will notify the Depositor in writing of any change in its fee
 schedule.

 (l) This Agreement and the Custodial Account created hereby shall be subject to
 the applicable laws, rules and regulations, as the same may from time to time
 be amended, of the Federal government and the Commonwealth of Massachusetts and
 the agencies and instrumentalities of each having jurisdiction thereof, and
 shall be governed by and construed, administered and enforced according to the
 law of the Commonwealth of Massachusetts. All contributions to the Custodial
 Account shall be deemed to take place in the Commonwealth of Massachusetts.

 (m) The Custodian and Depositor hereby waive and agree to waive right to trial
 by jury in an action or proceeding instituted in respect to this Custodial
 Account. The Depositor further agrees that the venue of any litigation between
 him and the Custodian with respect to the Custodial Account shall be in the
 County of Suffolk, Commonwealth of Massachusetts.

 (n) All communications or notices required or permitted to be given herein
 shall be deemed to be given upon receipt by the Custodian at P. O. Box 8502,
 Boston, MA 02266-8502, by the Trust at 227 W. Monroe St., #3000, Chicago, IL,
 60606, or the Depositor at his most recent address shown in the Custodian's
 records. The Depositor agrees to advise the Custodian promptly, in writing, of
 any change of address.

 (o) Subject to the last paragraph of this subparagraph (o), the Depositor may
 revoke the Custodial Account established hereunder by mailing or delivering a
 written notice of revocation to the Custodian within seven days after the
 Depositor first receives the Disclosure Statement related to the Custodial
 Account. Mailed notice is treated as given to the Custodian on the date of the
 postmark (or on the date of Post Office certification or registration in the
 case of notice sent by certified or registered mail). Upon timely revocation,
 the Depositor will receive a payment equal to the initial contribution, without
 adjustment for administrative expenses, commissions or sales charges,
 fluctuations in market value or other changes. The Depositor may certify in the
 Application that the Depositor received the Disclosure Statement related to the
 Custodial Account at least seven days before signing the Application to
 establish the Custodial Account, and the Custodian may rely on such
 certification.

 (p) The Depositor may in writing appoint an investment advisor with respect to
 the Custodial Account on a form acceptable to the Custodian and the Trust. The
 investment advisor's appointment will be in effect until written notice to the
 contrary is received by the Custodian and the Trust. While an investment
 advisor's appointment is in effect, the investment advisor may issue investment
 directions or may issue orders for the sale or purchase of shares of one or
 more Funds to the Trust, and the Trust and its agents will be fully protected
 in carrying out such investment directions or orders to the same extent as if
 they had been given by the Depositor. The Depositor's appointment of any
 investment advisor will also be deemed to be instructions to

                                      26
<PAGE>
 
 the Custodian and the Trust to pay such investment advisor's fees to the
 investment advisor from the Custodial Account hereunder without additional
 authorization by the Depositor or the Custodian.

8. The Trust

 (a) The Depositor delegates to the Trust the power with respect to this
 Agreement: (i) to remove the Custodian and select a successor Custodian; and
 (ii) to amend this Agreement as provided in paragraph 9.

 (b) The powers herein delegated to the Trust shall be exercised by such officer
 thereof as the Trust may designate from time to time, and shall be exercised
 only when similarly exercised with respect to all other Depositors establishing
 IRA accounts.

 (c) Neither the Trust nor any officer, director, trustee, board, committee,
 employee or member of the Trust shall incur any liability of any nature to the
 Depositor or beneficiary or other person in connection with any act done or
 omitted to be done in good faith in the exercise of any power or authority
 herein delegated to the Trust.

 (d) If the Trust shall hereafter determine that it is no longer desirable for
 the Trust to continue to exercise any of the powers hereby delegated to the
 Trust, it may relieve itself of any further responsibilities hereunder by
 notice in writing to the Depositor and the Custodian at least 60 days before
 the date on which the Trust proposes to discontinue the exercise of the powers
 delegated to it.

9. Amendment and Termination.

 (a) The Depositor delegates to the Trust the power to amend this Agreement
 (including retroactive amendment). A copy of any such amendment shall be
 furnished to the Custodian, and no such amendment shall have the effect of
 increasing the duties or obligations of the Custodian until it has been
 approved by the Custodian. A copy of any such amendment shall also be furnished
 to the Depositor, but no delay in furnishing such copy shall affect the
 effectiveness of such amendment.

 (b) The Depositor may amend his/her Application (including retroactive
 amendment) by submitting to the Custodian (i) a copy of such amended
 Application, and (ii) evidence satisfactory to the Custodian that the Agreement
 as amended by such amended Application will continue to qualify as a Roth
 Individual Retirement Account under the provisions of section 408A of the Code.

 (c) No amendment shall be effective if it would cause or permit (i) any part of
 the Custodial Account to be diverted to any purpose that is not for the
 exclusive benefit of the Depositor and his beneficiaries; (ii) the Depositor to
 be deprived of any portion of his interest in the Custodial Account, unless
 such action is taken in order to satisfy qualification requirements under the
 Code; or (iii) the imposition of an additional duty on the Custodian without
 its written consent.

 (d) The Depositor reserves the right to terminate his adoption of this
 Agreement by instrument in writing signed by him and filed with the Custodian.

 (e) In the event that the assets of any investment company (including any
 series of the Trust) in which the Custodial Account is invested are transferred
 to or acquired by any other investment company or other commingled investment
 fund which is a permissible investment for an individual retirement account, by
 merger or otherwise, the Trust may make such amendments to this Agreement, or
 take such other action, as it may determined to be necessary or appropriate to
 accomplish such transaction and the exchange of Fund Shares for shares or other
 appropriate units of ownership in such successor fund. The consent of the
 Depositor shall not be required for any such amendment or action, but the
 Depositor shall be promptly notified thereof, and shall have the right to
 withdraw the funds in the Custodial Account without fee, charge, load or
 penalty of any kind.

10. Definitions.

Whenever used in this Agreement, the following terms shall have the meanings set
forth below unless otherwise expressly provided herein:

 (a) Act. The Employee Retirement Income Security Act of 1974, as amended from
 time to time.

                                      27
<PAGE>
 
Custodial Agreement for a Roth IRA, continued


 (b) Agreement. This Custodial Agreement for a Roth IRA Account, including the
 Application, as amended from time to time.

 (c) Application. The IRA Application Form, constituting an agreement between
 the Depositor and the Custodian, by which the Depositor adopts this Agreement.

 (d) Code. The Internal Revenue Code of 1986, as amended from time to time.
 Reference to a section of the Code shall include that section and any
 comparable section or sections of any future legislation that amends,
 supplements or supersedes that section.

 (e) Custodial Account. The account established for the Depositor pursuant to
 this Agreement.

 (f) Custodian. The bank named in the Application.

 (g) Depositor. The individual who adopts this Agreement as provided therein.

 (h) Fund Shares. Shares issued by the Trust or shares of any other regulated
 investment company for which the Custodian acts as transfer agent and which may
 be available hereunder from time to time pursuant to an agreement between the
 Custodian and the Trust. No Fund shall be available for investment under this
 Agreement (i) before the date the prospectus for that Fund discloses its
 availability, (ii) with respect to any Depositor who resides in any state or
 other jurisdiction in which shares of the Fund are not available for sale, or
 (iii) with respect to any Depositor not eligible to purchase Fund shares
 directly, when sales of Fund shares are restricted.

 (i) Trust. Acorn Investment Trust, a regulated investment company.

11. Conflict in Provisions. To the extent that any of the provisions of Article 
IX shall conflict with the provisions of Articles V, VI, or VIII, the provisions
of Article IX shall prevail.

12. Loss of Exemption. If the Custodian receives notice that the Custodial
Account has lost its tax-exempt status under section 408A of the Code for any
reason, including by reason of a transaction prohibited by section 4975 of the
Code, the Custodian shall distribute to the Depositor the entire balance in the
Account, in cash or in kind, in the sole discretion of the Custodian no later
than 90 days after the date the Custodian receives such notice.

                                      28
<PAGE>
 
Acorn
____________________
     Family of Funds
WAM Brokerage Services, L.L.C.
P.O. Box 8502
Boston, MA 02266-8502
1-800-962-1585

IRAS1098

<PAGE>
                                                                    Exhibit 14.2
 
Acorn Family of Funds IRA                                 P.O. Box 8502
                                                          Boston, Ma  02266-8502


SPECIAL SUBSCRIPTION OFFER IRA APPLICATION

     Please use this application only to open a new Traditional IRA, Roth IRA,
     SEP-IRA or SIMPLE IRA account with Acorn Twenty or Acorn Foreign Forty. You
     may transfer money from an existing ira account or existing Acorn ira or
     employer-sponsored plan to Acorn Twenty or Acorn Foreign Forty only on or
     after November 23, 1998.

     Please note: You may only use regular contribution checks to establish your
     new ira account during the subscription period. Conversions, transfers or
     rollovers will be accepted only after the funds begin operations on
     November 23, 1998.

     If you have questions, or would like ira information about our other Acorn
     products, please call us at 1-800-9ACORN9 (1-800-922-6769), weekdays,
     8:00am-4:30pm, Central time. Please be sure to print your information on
     this application, then simply sign and return it to us in the postage-paid
     envelope we've provided or mail it to the address above.

================================================================================

1    Social Security or Tax Identification Number

     Please provide your social security or tax identification number. To
     invest, you must be a U.S. citizen or a non-citizen residing in the U.S.

     ___ ___ ___ ___ ___ ___ ___ ___ ___
     Social Security Number or Tax id Number used for tax reporting

[_]  U.S. Citizen     [_]  Non-citizen residing in the U.S.
 
2    Account Registration

     Please provide your personal information as you would like it to appear on
     your IRA account. The National Association of Securities Dealers (NASD)
     requires us to ask for your occupation, employer's name, employer's
     address, and whether or not you are affiliated with or work for a member of
     the nasd.

     ---------------------------------------------------------------------------
     Name (first, middle, last)

      
     ---------------------------------------------------------------------------
     Street address


     ---------------------------------------  ------------------  --------------
     City                                     State               Zip


     (    )                                   (    )
      ---- -------------------------------     ---- ----------------------------
     Daytime phone                            Evening phone

                  /          /
     ------------   --------   ----------
     Date of birth


     -------------------------------------
     e-mail address


     ---------------------------------------------------------------------------
     Your occupation


     ---------------------------------------------------------------------------
     Employer


     ---------------------------------------------------------------------------
     Employer's address


[_]  I'm affiliated with or work for a member of the NASD.

3    IRA Type

     Note: This Form For Regular Contributions Only.
     Please check the appropriate box for the type of IRA. See Disclosure
     Statement for more details on IRA account types.

[_]  Traditional IRA  [_]  SEP-IRA

[_]  Roth IRA         [_]  SIMPLE IRA

Your ira application and investment check must be received by the close of
business on November 20, 1998, to receive the opening nav of $10.00 per share.
On November 23, your check will be processed and the Funds will commence
operations. If we receive your investment after the close of business on
November 20, you will receive the nav next calculated after receipt of your
investment.

4    Choose Your Investment

     Indicate in which fund you would like us to invest your contribution--Acorn
     Twenty and/or Acorn Foreign Forty. Each new account requires a $5 set-up
     fee per fund. Each Fund has an initial minimum investment of $1,000.

[_]  Acorn Twenty                                    $
                                                      --------------------------
[_]  Acorn Foreign Forty                             $
                                                      --------------------------
     Set-Up Fee ($5 per fund)                        $
                                                      --------------------------
     Total                                           $
                                                      --------------------------

     Make your checks payable to State Street Bank and Trust Company and write
     your contribution year and the appropriate fund name on the check.
     The Acorn funds do not accept third party checks, credit cards or credit
     card checks.

5    How Did You Hear About Us?

     If you are not a current Acorn shareholder, please tell us how you heard
     about the new Funds.

[_]  Press mention (specify) __________
[_]  Referred by friend
[_]  Referred by advisor
[_]  Advertisement - Mutual Funds Magazine
[_]  Advertisement - Money Magazine
[_]  Advertisement - Worth Magazine
[_]  Advertisement - Wall Street Journal
[_]  Direct mail
[_]  Internet/World wide web (specify) __________
[_]  Other
<PAGE>

 
6    Automatic Investment Plan

     Complete this section if you would like to easily add to your Acorn ira
     through automatic monthly or quarterly investments. You will need to attach
     a voided check from your checking account for Acorn to set up the
     investment plan. The minimum automatic investment is $100; the annual
     maximum investment for an ira is $2,000. Monthly automatic investments are
     withdrawn from your bank account on or about the 15th of the month;
     quarterly investments are withdrawn from your bank account in January,
     April, July and October.

[_]  Acorn Twenty                    $_____________
[_]  monthly                    [_]  quarterly
                                
[_]  Acorn Foreign Forty             $_____________
[_]  monthly                    [_]  quarterly

7    IRA Beneficiary Designation

     Please indicate your beneficiaries. Attach additional instructions for
     beneficiaries as necessary. Share percentages must be whole, not fractional
     numbers, and must add up to 100%. Primary beneficiaries will initially
     receive payment of the IRA account upon your death. If any beneficiary is a
     trust, please indicate the trust's name and address, the date of the trust,
     and the trustee's name. You must also furnish State Street Bank, the
     Custodian, with either a copy of the trust agreement, or certain other
     information in accordance with IRS regulations. Contact an Acorn account
     representative at 1-800-962-1585 for details. Contingent beneficiaries will
     receive payment of the IRA account if no primary beneficiary is living at
     the time of your death. Payment to the primary and contingent beneficiaries
     will be made according to the rules of succession described in the
     signature section of your application.

     Your Primary Beneficiaries

     
     ---------------------------------------------------------------------------
     1. Name (first, middle, last)


     ---------------------------------------------------------------------------
     Share %                           Relationship


     ----------------------------------
     Date of birth (month, day, year)


     ---------------------------------------------------------------------------
     2. Name (first, middle, last)


     ---------------------------------------------------------------------------
     Share %                           Relationship


     ----------------------------------
     Date of birth (month, day, year)


     Your Contingent Beneficiaries


     ---------------------------------------------------------------------------
     1. Name (first, middle, last)


     ---------------------------------------------------------------------------
     Share %                           Relationship


     ----------------------------------
     Date of birth (month, day, year)


     ---------------------------------------------------------------------------
     2. Name (first, middle, last)


     ---------------------------------------------------------------------------
     Share %                           Relationship


     ----------------------------------
     Date of birth (month, day, year)

8    Agreement and Signature(s)

     By signing this application, I certify that:
 
     I understand that the annual IRA maintenance fee of $10 per fund account
     will be separately billed or collected by redeeming sufficient shares from
     each fund account. (This fee will be waived for 1998 for new Acorn Twenty
     or Acorn Foreign Forty ira accounts opened during the subscription period.)
 
     A $10 fee will apply for each disbursement other than an automatic
     installment payment.
 
     Acorn may change the fee schedule from time to time, as provided in the
     Custodial Agreement. Acceptance will be evidenced by a Letter of Acceptance
     sent by or on behalf of Acorn and State Street Bank and Trust Company
     (SSB&T).

     I understand that if more than one beneficiary is named and no percentages
     are indicated, payment shall be made in equal shares to my primary
     beneficiary(ies) who survives me. If a percentage is indicated and a
     primary beneficiary(ies) does not survive me, the percentage of that
     beneficiary's designated share shall be divided equally among the surviving
     primary beneficiary(ies).

     I understand that if I choose not to designate any beneficiary(ies), my
     beneficiary will be my estate (unless state law requires otherwise). I am
     aware that my beneficiary designation becomes effective when delivered to
     Acorn and will remain in effect until I deliver to Acorn another
     beneficiary designation with a later date.

     If I have named a trust as my beneficiary, I understand that I may be
     treated as having no beneficiary for minimum distribution purposes unless I
     furnish the Custodian with a copy of the trust or certain other
     information.

     I hereby adopt the Acorn Traditional or Roth IRA, as applicable, appointing
     SSB&T as Custodian and as agent to perform administrative services.
     Although SSB&T is a bank, I recognize that neither Acorn Investment Trust
     nor any mutual fund in which this IRA may be invested is a bank, and that
     mutual fund shares are not backed or guaranteed by any bank or insured by
     the FDIC. This agreement shall be construed, administered and enforced
     according to the laws of the Commonwealth of Massachusetts, except as
     superseded by federal law or statute.

     If this is a SEP-IRA, I further certify that I have, or my employer has,
     completed and executed Form 5305-sep and furnished to employees all
     materials required by applicable Department of Labor regulations. I further
     certify that, if my employer has adopted a Salary Reduction sep prior to
     1997, my employer has completed and executed Form 5305-a-sep and I have
     entered into a salary reduction agreement.

     I have received and read the prospectus for Acorn Twenty and Acorn Foreign
     Forty, the fund(s) in which I am making a contribution, and have read and
     understand the applicable IRA Custodial Agreement and Disclosure Statement.
     I hereby certify under penalties of perjury that my Social Security Number
     is correct and that I am of legal age to enter into this agreement.

     By signing below, I hereby consent to the terms of the Custodial Agreement
     for an Acorn Traditional IRA or Roth IRA, as applicable, and name the
     beneficiary(ies) I have designated in the application.

     Signature(s)

     X
      --------------------------------------------------------------------------
     Signature (sign exactly as name appears in Account Registration)    Date

<TABLE> <S> <C>

<PAGE>
<ARTICLE> 6
<LEGEND>
The following information is extracted from and qualified by reference to 
registrant's report on form N-SAR for the period ended June 30, 1998 and the
unaudited financial statements included in registrant's semi-annual report to 
shareholders.
</LEGEND>
<SERIES>   
   <NUMBER>   01 
   <NAME>     Acorn Fund 
<MULTIPLIER>  1,000 
       
<S>                             <C>
<PERIOD-TYPE>                   YEAR
<FISCAL-YEAR-END>                         DEC-31-1998
<PERIOD-END>                              JUN-30-1998
<INVESTMENTS-AT-COST>                         2238807
<INVESTMENTS-AT-VALUE>                        3969816
<RECEIVABLES>                                   22012
<ASSETS-OTHER>                                    126
<OTHER-ITEMS-ASSETS>                               68
<TOTAL-ASSETS>                                3992022
<PAYABLE-FOR-SECURITIES>                        21623
<SENIOR-LONG-TERM-DEBT>                             0
<OTHER-ITEMS-LIABILITIES>                        1709
<TOTAL-LIABILITIES>                             23332
<SENIOR-EQUITY>                                     0
<PAID-IN-CAPITAL-COMMON>                      2066902
<SHARES-COMMON-STOCK>                          212102
<SHARES-COMMON-PRIOR>                          216645
<ACCUMULATED-NII-CURRENT>                        1229
<OVERDISTRIBUTION-NII>                              0
<ACCUMULATED-NET-GAINS>                        170974
<OVERDISTRIBUTION-GAINS>                            0
<ACCUM-APPREC-OR-DEPREC>                      1729585
<NET-ASSETS>                                  3968690
<DIVIDEND-INCOME>                               16308
<INTEREST-INCOME>                                6598
<OTHER-INCOME>                                      0
<EXPENSES-NET>                                  15891
<NET-INVESTMENT-INCOME>                          7015
<REALIZED-GAINS-CURRENT>                       172951
<APPREC-INCREASE-CURRENT>                      241698
<NET-CHANGE-FROM-OPS>                          421664
<EQUALIZATION>                                      0
<DISTRIBUTIONS-OF-INCOME>                        6284
<DISTRIBUTIONS-OF-GAINS>                        48180
<DISTRIBUTIONS-OTHER>                               0
<NUMBER-OF-SHARES-SOLD>                         14971
<NUMBER-OF-SHARES-REDEEMED>                     22218
<SHARES-REINVESTED>                              2704
<NET-CHANGE-IN-ASSETS>                         287233
<ACCUMULATED-NII-PRIOR>                           498
<ACCUMULATED-GAINS-PRIOR>                       47522
<OVERDISTRIB-NII-PRIOR>                             0
<OVERDIST-NET-GAINS-PRIOR>                          0 
<GROSS-ADVISORY-FEES>                           13073    
<INTEREST-EXPENSE>                                  0
<GROSS-EXPENSE>                                 15891
<AVERAGE-NET-ASSETS>                          3863831 
<PER-SHARE-NAV-BEGIN>                           16.99
<PER-SHARE-NII>                                   .03
<PER-SHARE-GAIN-APPREC>                          1.95
<PER-SHARE-DIVIDEND>                              .03
<PER-SHARE-DISTRIBUTIONS>                         .23
<RETURNS-OF-CAPITAL>                                0
<PER-SHARE-NAV-END>                             18.71
<EXPENSE-RATIO>                                   .83
<AVG-DEBT-OUTSTANDING>                              0
<AVG-DEBT-PER-SHARE>                                0
        

</TABLE>

<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 6
<LEGEND>
The following information is extracted from and qualified by reference to
registrant's report on form N-SAR for the period ended June 30, 1998 and the
unaudited financial statements included in registrant's semi-annual report to
shareholders.
</LEGEND>
<SERIES>
   <NUMBER>   02
   <NAME>     ACORN INTERNATIONAL
<MULTIPLIER>  1,000
       
<S>                             <C>
<PERIOD-TYPE>                   6-MOS
<FISCAL-YEAR-END>                         DEC-31-1998
<PERIOD-END>                              JUN-30-1998
<INVESTMENTS-AT-COST>                         1238941
<INVESTMENTS-AT-VALUE>                        1837913
<RECEIVABLES>                                   31793
<ASSETS-OTHER>                                   1636
<OTHER-ITEMS-ASSETS>                             1740
<TOTAL-ASSETS>                                1873082
<PAYABLE-FOR-SECURITIES>                         9760
<SENIOR-LONG-TERM-DEBT>                             0
<OTHER-ITEMS-LIABILITIES>                        2037
<TOTAL-LIABILITIES>                             11797
<SENIOR-EQUITY>                                     0
<PAID-IN-CAPITAL-COMMON>                      1261635
<SHARES-COMMON-STOCK>                           85629
<SHARES-COMMON-PRIOR>                           88273
<ACCUMULATED-NII-CURRENT>                        2290
<OVERDISTRIBUTION-NII>                              0
<ACCUMULATED-NET-GAINS>                            40
<OVERDISTRIBUTION-GAINS>                            0
<ACCUM-APPREC-OR-DEPREC>                       597320
<NET-ASSETS>                                  1861285
<DIVIDEND-INCOME>                               17546
<INTEREST-INCOME>                                3174
<OTHER-INCOME>                                      0
<EXPENSES-NET>                                   9805
<NET-INVESTMENT-INCOME>                         10915
<REALIZED-GAINS-CURRENT>                        20031
<APPREC-INCREASE-CURRENT>                      287282
<NET-CHANGE-FROM-OPS>                          318228
<EQUALIZATION>                                      0
<DISTRIBUTIONS-OF-INCOME>                       12611
<DISTRIBUTIONS-OF-GAINS>                        22701
<DISTRIBUTIONS-OTHER>                               0
<NUMBER-OF-SHARES-SOLD>                         11167
<NUMBER-OF-SHARES-REDEEMED>                     15351
<SHARES-REINVESTED>                              1540
<NET-CHANGE-IN-ASSETS>                         238346
<ACCUMULATED-NII-PRIOR>                          3986
<ACCUMULATED-GAINS-PRIOR>                       15568
<OVERDISTRIB-NII-PRIOR>                             0
<OVERDIST-NET-GAINS-PRIOR>                          0
<GROSS-ADVISORY-FEES>                            7192
<INTEREST-EXPENSE>                                  0
<GROSS-EXPENSE>                                  9805
<AVERAGE-NET-ASSETS>                          1762077
<PER-SHARE-NAV-BEGIN>                           18.39
<PER-SHARE-NII>                                   .13
<PER-SHARE-GAIN-APPREC>                          3.64
<PER-SHARE-DIVIDEND>                              .15
<PER-SHARE-DISTRIBUTIONS>                         .27
<RETURNS-OF-CAPITAL>                                0
<PER-SHARE-NAV-END>                             21.74
<EXPENSE-RATIO>                                  1.11
<AVG-DEBT-OUTSTANDING>                              0
<AVG-DEBT-PER-SHARE>                                0
        

</TABLE>

<TABLE> <S> <C>

<PAGE>
 
<ARTICLE> 6
<LEGEND> 
The following information is extracted from and qualified by reference to
registrant's report on form N-SAR for the period ended June 30, 1998 and the
unaudited financial statements included in registrant's semi-annual report to
shareholders
</LEGEND>
<SERIES>   
   <NUMBER>   03 
   <NAME>     ACORN USA
<MULTIPLIER> 1,000 
       
<S>                             <C>
<PERIOD-TYPE>                   6-MOS
<FISCAL-YEAR-END>                         DEC-31-1998
<PERIOD-END>                              JUN-30-1998
<INVESTMENTS-AT-COST>                          245890
<INVESTMENTS-AT-VALUE>                         286586
<RECEIVABLES>                                    1234
<ASSETS-OTHER>                                     71
<OTHER-ITEMS-ASSETS>                                0
<TOTAL-ASSETS>                                 287891
<PAYABLE-FOR-SECURITIES>                         4580
<SENIOR-LONG-TERM-DEBT>                             0
<OTHER-ITEMS-LIABILITIES>                         685
<TOTAL-LIABILITIES>                              5265
<SENIOR-EQUITY>                                     0
<PAID-IN-CAPITAL-COMMON>                       223219
<SHARES-COMMON-STOCK>                           16537
<SHARES-COMMON-PRIOR>                           12212
<ACCUMULATED-NII-CURRENT>                       (547)
<OVERDISTRIBUTION-NII>                              0
<ACCUMULATED-NET-GAINS>                         19259
<OVERDISTRIBUTION-GAINS>                            0
<ACCUM-APPREC-OR-DEPREC>                        40695
<NET-ASSETS>                                   282626
<DIVIDEND-INCOME>                                 417
<INTEREST-INCOME>                                 457
<OTHER-INCOME>                                      0
<EXPENSES-NET>                                   1421
<NET-INVESTMENT-INCOME>                         (547)
<REALIZED-GAINS-CURRENT>                        19318
<APPREC-INCREASE-CURRENT>                        9329
<NET-CHANGE-FROM-OPS>                           28100
<EQUALIZATION>                                      0
<DISTRIBUTIONS-OF-INCOME>                           0
<DISTRIBUTIONS-OF-GAINS>                         1640
<DISTRIBUTIONS-OTHER>                               0
<NUMBER-OF-SHARES-SOLD>                          6461
<NUMBER-OF-SHARES-REDEEMED>                      2226
<SHARES-REINVESTED>                                90
<NET-CHANGE-IN-ASSETS>                          98002
<ACCUMULATED-NII-PRIOR>                             0
<ACCUMULATED-GAINS-PRIOR>                        1581
<OVERDISTRIB-NII-PRIOR>                             0
<OVERDIST-NET-GAINS-PRIOR>                          0
<GROSS-ADVISORY-FEES>                            1114
<INTEREST-EXPENSE>                                  0
<GROSS-EXPENSE>                                  1424
<AVERAGE-NET-ASSETS>                           238265
<PER-SHARE-NAV-BEGIN>                           15.12
<PER-SHARE-NII>                                 (.04)
<PER-SHARE-GAIN-APPREC>                          2.11
<PER-SHARE-DIVIDEND>                                0
<PER-SHARE-DISTRIBUTIONS>                         .10
<RETURNS-OF-CAPITAL>                                0
<PER-SHARE-NAV-END>                             17.09
<EXPENSE-RATIO>                                  1.20
<AVG-DEBT-OUTSTANDING>                              0
<AVG-DEBT-PER-SHARE>                                0
        

</TABLE>


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