SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549
                           --------------------------
                                   SCHEDULE TO
            Tender Offer Statement Under Section 14(d)(1) or 13(e)(1)
                     of the Securities Exchange Act of 1934

                                (Amendment No. 6)
                           --------------------------
                               PRIMARK CORPORATION
                       (Name of Subject Company (Issuer))
                           --------------------------
                         MARQUEE ACQUISITION CORPORATION
                             THE THOMSON CORPORATION
                      (Names of Filing Persons (Offerors))
                           --------------------------
                      Common Stock, No Par Value Per Share
                         (Title of Class of Securities)
                           --------------------------
                                    741903108
                      (CUSIP Number of Class of Securities)

                             Michael S. Harris, Esq.
                             The Thomson Corporation
                        Metro Center at One Station Place
                           Stamford Connecticut 06902
                            Telephone (203) 969-8700

  (Name, Address and Telephone Number of Persons Authorized to Receive Notices
                 and Communications on Behalf of filing persons)
                           --------------------------
                                    Copy to:
                             David W. Heleniak, Esq.
                               Shearman & Sterling
                              599 Lexington Avenue
                            New York, New York 10022
                                 (212) 848-4000

                            CALCULATION OF FILING FEE
================================================================================
       Transaction Valuation*                     Amount of Filing Fee**
- --------------------------------------------------------------------------------
           $913,518,708                                $182,703.74
================================================================================

*    Estimated for purposes of calculating the amount of the filing fee only.
     Calculated by multiplying $38.00, the per share tender offer price, by
     24,039,966, the sum of the 20,308,103 currently outstanding shares of
     Common Stock sought in the Offer and the 3,731,863 shares of Common Stock
     subject to options that vested as of June 12, 2000.
**   Calculated as 1/50 of 1% of the transaction value.
[X]  Check the box if any part of the fee is offset as provided by Rule
     0-11(a)(2) and identify the filing with which the offsetting fee was
     previously paid. Identify the previous filing by registration statement
     number, or the Form or Schedule and the date of its filing.

Amount Previously Paid:   $182,703.74     Filing Party: The Thomson Corporation,
                                                        Marquee Acquisition
                                                        Corporation
Form or Registration No.: Schedule TO     Date Filed:   June 14, 2000
[ ]  Check the box if the filing relates solely to preliminary communications
     made before the commencement of a tender offer.
Check the appropriate boxes to designate any transactions to which the statement
relates:
[X]  third-party tender offer subject to Rule 14d-1.
[ ]  issuer tender offer subject to Rule 13e-4.
[ ]  going-private transaction subject to Rule 13e-3.
[X]  amendment to Schedule 13D under Rule 13d-2.
Check the following box if the filing is a final amendment reporting the results
of the tender offer: [ ]


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              This Amendment No. 6 (the "Amendment") amends and supplements the
Tender Offer Statement on Schedule TO filed with the Securities and Exchange
Commission on June 14, 2000 (the "Schedule TO"), by Marquee Acquisition
Corporation, a Michigan corporation ("Purchaser") and an indirect wholly owned
subsidiary of The Thomson Corporation, a corporation organized under the laws of
Ontario, Canada ("Thomson"). The Schedule TO relates to the offer by Purchaser
to purchase all outstanding shares of Common Stock, no par value, including
associated common stock purchase rights (together, the "Shares"), of Primark
Corporation, a Michigan corporation (the "Company"), at a purchase price of
$38.00 per Share, net to each seller in cash, upon the terms and subject to the
conditions set forth in the Offer to Purchase dated June 14, 2000 (the "Offer to
Purchase") and in the related Letter of Transmittal, copies of which are filed
as Exhibits (a)(1) and (a)(2) to the Schedule TO (which, together with any
amendments or supplements thereto, collectively constitute the "Offer").
Capitalized terms used and not defined herein shall have the meanings ascribed
to such terms in the Offer to Purchase or in the Schedule TO.

Item 4.       Terms of the Transaction.

              Item 4 of the Schedule TO is hereby amended and supplemented by
the following:

              On August 30, 2000, Thomson issued a press release announcing the
extension of the Offer until 5:00 p.m., Eastern Daylight Time, on Tuesday,
September 12, 2000. Thomson also announced that it had been advised by Morgan
Stanley Dean Witter, the dealer manager for the Offer, that as of 5:00 p.m.,
EDT, on August 28, 2000, approximately 16,111,076 Common Shares had been
tendered. The foregoing description of the press release which is attached
hereto as Exhibit (a)(13) is incorporated by reference herein.





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              After due inquiry and to the best of my knowledge and belief, I
certify that the information set forth in this statement is true, complete and
correct.

Dated:  August 30, 2000

                                     MARQUEE ACQUISITION CORPORATION


                                     By:   /s/ Michael S. Harris
                                        ----------------------------------------
                                        Name:  Michael S. Harris
                                        Title: Vice President




                                     THE THOMSON CORPORATION


                                     By:   /s/ Michael S. Harris
                                        ----------------------------------------
                                        Name:  Michael S. Harris
                                        Title: Senior Vice President and
                                               General Counsel



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                                  EXHIBIT INDEX






Exhibit No.
(a)(1)        Offer to Purchase, dated June 14, 2000.*
(a)(2)        Form of Letter of Transmittal.*
(a)(3)        Form of Notice of Guaranteed Delivery.*
(a)(4)        Form of Letter to Brokers, Dealers, Commercial Banks, Trust
              Companies and Other Nominees.*
(a)(5)        Form of Letter from Brokers, Dealers, Commercial Banks, Trust
              Companies and Nominees to Clients.*
(a)(6)        Form of Guidelines for Certification of Taxpayer Identification
              Number on Substitute Form W-9.*
(a)(7)        Summary Advertisement as published in The Wall Street Journal on
              June 14, 2000.*
(a)(8)        Joint Press Release issued by Thomson and the Company on June 5,
              2000.*
(a)(9)        Press Release issued by Thomson on June 22, 2000.**
(a)(10)       Joint Press Release issued by Thomson and the Company on June 28,
              2000.***
(a)(11)       Press Release issued by Thomson on July 12, 2000.****
(a)(12)       Press Release issued by Thomson on August 2, 2000.*****
(a)(13)       Press Release issued by Thomson on August 30, 2000.
(b)           None.
(c)           None.
(d)(1)        Agreement and Plan of Merger, dated as of June 5, 2000, among
              Thomson, Purchaser and the Company.*
(d)(2)        Confidentiality Agreement dated April 4, 2000, between Thomson and
              the Company.*
(d)(3)        Shareholders Agreement, dated June 5, 2000, among Thomson,
              Purchaser, Joseph E. Kasputys, Stephen H. Curran and Michael R.
              Kargula.*
(d)(4)        Guarantee, dated June 5, 2000, of Thomson in favor of Joseph E.
              Kasputys.*
(d)(5)        Letter Agreement, dated June 5, 2000, between Primark Corporation
              and Stephen H. Curran.*
(d)(6)        Letter Agreement, dated June 5, 2000, between Primark Corporation
              and Michael R. Kargula.*
(d)(7)        Letter Agreement, dated June 5, 2000, between Primark Corporation
              and Joseph E. Kasputys.*
(g)           None.
(h)           None.

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


              * Incorporated by reference to Thomson's Schedule TO, filed June
14, 2000.

              ** Incorporated by reference to Thomson's Schedule TO/A, filed
June 23, 2000.

              *** Incorporated by reference to Thomson's Schedule TO/A, filed
June 28, 2000.

              **** Incorporated by reference to Thomson's Schedule TO/A, filed
July 13, 2000.

              ***** Incorporated by reference to Thomson's Schedule TO/A, filed
August 2, 2000.


The Thomson Corporation                                           [LOGO OMITTED]
Toronto Dominion Bank Tower, Suite 2706
PO Box 24, Toronto-Dominion Centre
Toronto, Ontario M5K 1A1
Tel (416) 360-8700   Fax (416) 360-8812
www.thomson.com


News Release


Investor Contact:                       Media Contact:
- ----------------                        -------------
John Kechejian                          Janey Loyd
Vice President, Investor Relations      Vice President, Corporate Communications
(203) 969-8700                          (203) 969-8700
john.kechejian@thomson.com              janey.loyd@thomson.com

                                        Jason Stewart
                                        Director, Public Relations
                                        (203) 969-8700
                                        jason.stewart@thomson.com


For Immediate Release
- --------------------------------------------------------------------------------

                         THE THOMSON CORPORATION EXTENDS
                    EQUITY AND DEBT TENDER OFFERS FOR PRIMARK

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

              TORONTO, ONTARIO, August 30, 2000 - The Thomson Corporation (TSE:
TOC) announced today that Marquee Acquisition Corporation ("Marquee"), a wholly
owned subsidiary of Thomson, is extending its offer to acquire all outstanding
shares of common stock of Primark Corporation until Tuesday, September 12, 2000
at 5:00 p.m. Eastern Daylight Time (EDT). In accordance with the terms of the
Offer to Purchase, dated June 14, 2000, Marquee is extending the offer to allow
the satisfaction of certain closing conditions. The offer to acquire the common
stock of Primark was previously scheduled to expire at 5:00 p.m. EDT on
Wednesday, August 30, 2000.

              In addition, Thomson announced that Marquee is extending its offer
to acquire all of the outstanding Primark 9 1/4% Senior Subordinated Notes due
2008 (the "Notes") until Wednesday, September 13, 2000 at 5:00 p.m. EDT. The
offer to acquire the Notes was previously scheduled to expire at 5:00 p.m. EDT
on Thursday, August 31, 2000.

              Based on the latest count of tendered shares and Notes, as of 5:00
p.m. EDT on August 28, 2000, 16,111,076 shares of Primark common stock
(constituting approximately 79% of the outstanding common stock) had been
tendered and not withdrawn, and approximately US$149.9 million in the aggregate
principal amount of the Notes (constituting just over 99.9% of the outstanding
Notes) had been tendered and not withdrawn.

              The tender offer for the Primark common stock is being made
through, and the foregoing announcement is qualified in its entirety by
reference to, Marquee's Offer to Purchase dated June 14, 2000, and the related
letter of transmittal. The tender offer for the Notes is being made through, and
the foregoing announcement is qualified in its entirety by reference to,
Marquee's Offer to Purchase and Consent Solicitation Statement dated June 22,
2000, and the related letter of transmittal. Primark stockholders and
noteholders should read the applicable Offer to Purchase and related letter of
transmittal in their entirety prior to making any decision as to the respective
tender offers.


                                     -more-




Pg. 2 of 2
The Thomson Corporation Extends
Equity and Debt Tender Offers for Primark




              The Thomson Corporation (www.thomson.com), with 1999 revenues of
US$5.8 billion, is a leading, global e-information and solutions company in the
business and professional marketplace. Thomson's common shares are listed on the
Toronto and London Stock Exchanges.


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