CERTIFICATIONS PURSUANT TO SECTION 906 OF THE
                          SARBANES-OXLEY ACT OF 2002

David P. Butler and Gerard K. O'Reilly, Co-Principal Executive Officers, and
Gregory K. Hinkle, Principal Financial Officer, of DFA Investment Dimensions
Group Inc., a Maryland corporation (the "Registrant"), each certify that:

     1.  The Registrant's periodic report on Form N-CSR for the period ended
         October 31, 2019 (the "Report") fully complies with the requirements
         of Section 13(a) or Section 15(d) of the Securities Exchange Act of
         1934, as amended, as applicable; and

     2.  The information contained in the Report fairly presents, in all
         material respects, the financial condition and results of operations
         of the Registrant.

By:  /s/ David P. Butler
     ---------------------------------------
     David P. Butler
     Co-Principal Executive Officer
     DFA Investment Dimensions Group Inc.

Date: January 6, 2020

By:  /s/ Gerard K. O'Reilly
     ---------------------------------------
     Gerard K. O'Reilly
     Co-Principal Executive Officer
     DFA Investment Dimensions Group Inc.

Date: January 6, 2020

By:  /s/ Gregory K. Hinkle
     ---------------------------------------
     Gregory K. Hinkle
     Principal Financial Officer
     DFA Investment Dimensions Group Inc.

Date: January 6, 2020