Form 8-A12B DFA INVESTMENT DIMENSION

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-A

FOR REGISTRATION OF CERTAIN CLASSES OF SECURITIES

PURSUANT TO SECTION 12 (b) OR (g) OF THE

SECURITIES EXCHANGE ACT OF 1934

(Exact name of registrant as specified in its charter)

Securities to be registered pursuant to Section 12(b) of the Act:

If this form relates to the registration of a class of securities pursuant to Section 12(b) of the Exchange Act and is effective pursuant to General Instruction A.(c) or (e), check the following box. [X]

If this form relates to the registration of a class of securities pursuant to Section 12(g) of the Exchange Act and is effective pursuant to General Instruction A.(d) or (e), check the following box. [  ]

If this form relates to the registration of a class of securities concurrently with a Regulation A offering, check the following box. [  ]

Securities Act registration statement or Regulation A offering statement file number to which this form relates: 002-73948

Securities to be registered pursuant to Section 12 (g) of the Act:

(Title of class)

INFORMATION REQUIRED IN REGISTRATION STATEMENT

Item 1. Descriptions of Registrant’s Securities to be Registered.

A description of the class of shares of common stock, par value of one cent ($0.01), of the series of DFA Investment Dimensions Group Inc. (the “Fund”) listed below to be registered hereunder is set forth in Post-Effective Amendment No. 266 to the Fund’s Registration Statement on Form N-1A (Commission File Nos. 002-73948; 811-03258), as filed with the Securities and Exchange Commission on February 27, 2026, which description is incorporated herein by reference.

The class of the series of the Fund that is registering securities, and its I.R.S. Employer Identification Number, is as follows:

Item 2. Exhibits

SIGNATURE

Pursuant to the requirements of Section 12 of the Securities Exchange Act of 1934, the registrant has duly caused this registration statement to be signed on its behalf by the undersigned, thereto duly authorized, as of this 29^th day of April, 2026.