CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

     We have issued our report dated April 22, 2008, accompanying the financial
statements of S&P Dividend Growth Opportunities Trust, Series 7 (included in Van
Kampen Unit Trusts, Series 636) as of December 31, 2007, and for the period from
January 10, 2007 (Initial Date of Deposit) through December 31, 2007 then ended
and the financial highlights for the period from January 10, 2007 (Initial Date
of Deposit) through December 31, 2007, contained in this Post-Effective
Amendment No. 1 to Form S-6 (File No. 333-139097) and Prospectus.

     We hereby consent to the use of the aforementioned report in this
Post-Effective Amendment and Prospectus and to the use of our name as it appears
under the caption "Other Matters-Independent Registered Public Accounting Firm".

                               GRANT THORNTON LLP

New York, New York
April 22, 2008