EXHIBIT NO. EX-99.h.3.w.1

                      DFA INVESTMENT DIMENSIONS GROUP INC.

                       THE HD U.S. LARGE COMPANY PORTFOLIO

                        FORM OF ADMINISTRATION AGREEMENT
                               ADDENDUM NUMBER ONE

     THIS ADDENDUM made this ___ day of ________, 2001, by and between DFA
INVESTMENT DIMENSIONS GROUP INC., a Maryland corporation (the "Fund"), on behalf
of:

                      "THE HD U.S. LARGE COMPANY PORTFOLIO"

(the "Portfolio"), a separate series of the Fund, and DIMENSIONAL FUND ADVISORS
INC., a Delaware corporation (the "Administrator").

     WHEREAS, the Fund and the Administrator have previously entered into an
Administration Agreement, dated July 26, 2000 (the "Administration Agreement"),
pursuant to which the Administrator has agreed to provide the services,
assistance and facilities of an administrator, and to perform various
administrative and other services for the Portfolio; and

     WHEREAS, the administrator has been informed by the Fund that the Portfolio
desires to change its name;

     NOW, THEREFORE, in consideration of the terms and conditions hereinafter
set forth, it is hereby agreed as follows:

     1.   The name of the Portfolio shall be changed from "The HD U.S. Large
Company Portfolio" to "HD U.S. Marketwide Portfolio," and all references in the
Administration Agreement to "The HD U.S. Large Company Portfolio" shall be
changed to "HD U.S. Marketwide Portfolio."

     2.   The effective date of this Addendum shall be August 1, 2001.

     3.   The parties hereby further agree that no other provisions of the
Administration Agreement are in any way modified by this Addendum, and that all
other provisions of the Administration Agreement remain in full force and
effect.

     IN WITNESS WHEREOF, the parties hereby have caused this Addendum to be
executed this ____ day of _______, 2001.

DFA INVESTMENT DIMENSIONS                     DIMENSIONAL FUND ADVISORS
GROUP INC.                                    INC.

By:                                           By:
    ----------------------------------------  ----------------------------------
     Michael T. Scardina                      Catherine L. Newell
     Vice President, Chief Financial Officer  Vice President and Secretary
     and Treasurer

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