<PAGE>
 
                                UNITED STATES
                     SECURITIES AND EXCHANGE COMMISSION

                            WASHINGTON, DC 20549

                                  FORM 10-Q/A
                               (AMENDMENT NO. 1)

   [X]  QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
                            EXCHANGE ACT OF 1934


              For the quarterly period ended September 30, 1998

   [_]  TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES
                            EXCHANGE ACT OF 1934


              For the Transition period from ________ to ________

              Commission File Number:                     0-25674


                      CBT GROUP PUBLIC LIMITED COMPANY
           (Exact name of registrant as specified in its charter)



        Republic of Ireland                              Not Applicable
        ---------------------------------------------------------------
(State or other jurisdiction of            (I.R.S. Employer Identification No.)
 incorporation or organization)


                            900 CHESAPEAKE DRIVE
                       REDWOOD CITY, CALIFORNIA 94063
        (Address of principal executive offices, including zip code)


                               (650) 817-5900
            (Registrant's telephone number, including area code)


Indicate by check mark whether Registrant (1) has filed all reports required to
be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during
the preceding 12 months (or for such shorter period that Registrant was required
to file such reports), and (2) has been subject to such filing requirements for
the past 90 days.

                               Yes [X]  No [_]


The number of American Depositary Shares (issued or issuable in exchange for
Registrant's issued and outstanding Ordinary Shares) outstanding as of October
31, 1998 was 44,355,890.
<PAGE>
 
                      CBT GROUP PUBLIC LIMITED COMPANY

                              TABLE OF CONTENTS

<TABLE> 
<CAPTION> 
                                                                                     Page
                                                                                    Number
                                                                                    ------
<S>           <C>                                                                  <C> 
PART I.        FINANCIAL INFORMATION

   Item 1.     Financial Statements

               Condensed Consolidated Balance Sheets as of December 31, 1997           3
               and as of September 30, 1998

               Condensed Consolidated Statements of Operations for the three           4
               and nine month periods ended September 30, 1997 and 1998

               Condensed Consolidated Statements of Cash Flows for the nine            5
               month periods ended September 30, 1997 and 1998

               Notes to Condensed Consolidated Financial Statements                    6
</TABLE> 

   This quarterly report on Form 10-Q/A ("Form 10Q/A") is being filed as
   Amendment No. 1 to the Registrant's Quarterly Report on Form 10-Q filed with
   the Secrities and Exchange Commission on November 16, 1998 ("Form 10-Q") for
   the purposes of amending Item 1 to include additional disclosure in the Notes
   to Condensed Consolidated Financial Statements.
                                        2
<PAGE>
 
PART I FINANCIAL INFORMATION
ITEM 1 FINANCIAL STATEMENTS

                                 CBT GROUP PLC
                     CONDENSED CONSOLIDATED BALANCE SHEETS
                            (dollars in thousands) 
<TABLE> 
<CAPTION> 
                                                                                   DECEMBER 31,           SEPTEMBER 30,
                                                                                       1997                   1998
                                                                                                          (Unaudited)
<S>                                                                               <C>                   <C>
                                           ASSETS
Current Assets
Cash                                                                                    $ 35,505                $ 63,086
Short term investments                                                                    36,038                  36,217
Accounts receivable, net                                                                  40,031                  43,484
Inventories                                                                                  615                     701
Deferred tax assets, net                                                                     140                     234
Prepaid expenses                                                                           4,198                   5,830
                                                                                        --------                --------
              Total Current assets                                                       116,527                 149,552
Intangible assets                                                                          5,600                   4,502
Property and equipment, net                                                               10,207                  16,569
Investment                                                                                   200                     550
Deferred tax assets, net                                                                     342                      47
Other assets                                                                               8,453                  13,883
                                                                                        --------                --------
              Total  assets                                                              141,329                 185,103
                                                                                        ========                ========
                                 LIABILITIES AND SHAREHOLDERS' EQUITY
Current Liabilities
Borrowings under bank overdraft facility and overdrafts                                       13                      54
Accounts Payable                                                                           4,820                   5,927
Accrued payroll and related expenses                                                       6,411                   3,579
Other accrued liabilities                                                                 16,715                  21,427
Deferred revenues                                                                          4,551                   1,859
                                                                                        --------                --------
                     Total Current Liabilities                                            32,510                  32,846
Non Current Liabilities
Other accrued liabilities                                                                    519                     287
Minority equity interest                                                                     622                     622
                                                                                        --------                --------
                     Total Non Current Liabilities                                         1,141                     909
Shareholders' Equity
Ordinary Shares: 30,000,000 shares authorized , IR37.5p par value, at                      6,372                   6,678
December 31, 1997 and 120,0000 shares authorized, par value IR9.375p at
September 30, 1998;
Issued and outstanding: 10,511,190 shares at December 31, 1997 and
44,213,526 shares at September 30, 1998
Additional paid-in-capital                                                                97,868                 126,432
Accumulated surplus                                                                        2,984                  17,302
Deferred compensation                                                                       (112)                      -
Cumulative translation adjustment                                                            566                     936
                                                                                        --------                --------
Shareholders' equity                                                                     107,678                 151,348
                                                                                        --------                --------
              Total liabilities and shareholders' equity                                 141,329                 185,103
                                                                                        ========                ========
</TABLE>
Note:  The condensed consolidated balance sheet at December 31, 1997 has been
derived from the audited financial statements at that date and has been restated
to reflect the acquisition of The ForeFront Group, Inc (see note 2 below). In
addition, the balance sheet does not include all of the information and
footnotes required by generally accepted accounting principles for complete
financial statements.

                                       3
<PAGE>
 
                                 CBT GROUP PLC
                                        
                CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS
               (dollars in thousands, except per share amounts)
                                        
<TABLE>
<CAPTION>
                                                     Three Months                        Nine Months
                                                     ------------                        -----------
                                                  Ended September 30,                Ended September 30,
                                                  -------------------                -------------------
                                                  1997           1998                1997           1998
                                                  ----           ----                ----           ----
                                             (Unaudited)       (Unaudited)       (Unaudited)     (Unaudited)
<S>                                         <C>               <C>               <C>             <C>
Revenues                                        $35,136          $35,182           $91,618         $119,963
Cost of revenues                                  5,657            5,998            15,511           18,639
                                                -------          -------           -------         --------
Gross profit                                     29,479           29,184            76,107          101,324
Operating expenses:
  Research and development                        5,105            5,762            14,267           18,756
  Sales and marketing                            14,680           17,684            40,923           53,174
  General and administrative                      2,624            4,179             8,588           10,987
  Acquired research and development               3,650               --             4,097               --
  Cost of acquisitions                              242               --             1,168            5,505
                                                -------          -------           -------         --------
    Total operating expenses                     26,301           27,625            69,043           88,422
                                                -------          -------           -------         --------
Income from operations                            3,178            1,559             7,064           12,902
Other income, net                                 2,599            1,786             3,819            3,689
                                                -------          -------           -------         --------
Income before provision for income taxes          5,777            3,345            10,883           16,591
Provision for income taxes                        1,043              468             2,379            2,273
                                                -------          -------           -------         --------
Net income                                        4,734            2,877             8,504           14,318
                                                =======          =======           =======         ========
Net income per equivalent ADS (1) - Basic         $0.12            $0.07             $0.21            $0.33
                                                =======          =======           =======         ========
ADSs used in computing net income per            40,984           43,944            40,146           43,262
 equivalent ADS - Basic                         =======          =======           =======         ========
Net income per equivalent ADS (1) -               $0.11            $0.06             $0.19            $0.31
 Diluted                                        =======          =======           =======         ========
ADSs used in computing net income per            44,983           46,498            44,247           46,222
 equivalent ADS - Diluted                       =======          =======           =======         ========
</TABLE>

(1)  Net income per equivalent ADS gives effect to the two-for-one split of
     Registrants' ADSs effected in March 1998. Prior periods have been restated
     to give effect to such split.

                                       4
<PAGE>
 
                                      CBT GROUP PLC
                      CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS
                               INCREASE (DECREASE) IN CASH
                                 (dollars in thousands)

<TABLE> 
<CAPTION> 
                                                                                  Nine Months Ended
                                                                                     September 30,
                                                                                 1997             1998
                                                                              -----------      -----------
                                                                              (Unaudited)      (Unaudited)
<S>                                                                           <C>              <C> 
CASH FLOWS FROM OPERATING ACTIVITIES
Net income                                                                     $ 8,504          $14,318
Adjustments to reconcile net income to net cash provided
 by operating activities:
 Depreciation and amortization                                                   3,096            4,306
 (Gain) / Loss on Disposal of Assets                                            (1,869)             178 
 Accrued interest on short-term investments                                        193              347
 Compensation Expense                                                               66              112
 Non cash acquired Research and Development costs                                4,097                -
 Changes in operating assets and liabilities:
  Accounts receivable                                                           (8,088)          (3,474)
  Inventories                                                                      (45)             (62)
  Deferred tax assets                                                                -              201
  Prepaid expenses and other assets                                             (3,962)          (7,091)
  Accounts payable                                                                 631            1,211
  Accrued payroll and related expenses and other accrued liabilities             3,256            1,651
  Deferred revenues                                                             (1,868)          (2,606)
                                                                               --------         --------
Net cash provided by operating activities                                        4,011            9,091
                                                                               --------         --------

CASH FLOWS FROM INVESTING ACTIVITIES
 Purchase of property and equipment                                             (4,207)          (9,814)
 Proceeds from disposal of property and equipment                                1,869                -
 Net Cash paid for Lantec acquisition                                           (1,803)               -
 Payments to acquire short-term investments                                     (1,390)         (78,980)
 Proceeds from disposal of investments                                               -           78,454
 Payments to acquire investment                                                   (200)            (350)
                                                                               --------         --------

 Net cash used in investing activities                                          (5,731)         (10,690)
                                                                               --------         --------

CASH FLOWS FROM FINANCING ACTIVITIES
 Repayment of bank loans                                                          (794)               -
 (Repayments) / Proceeds under bank overdraft facility                            (138)              41
 Proceeds from issuance of preferred shares in subsidiary                          605                -
 Proceeds from issuance of ordinary shares, net                                 11,238           28,870
                                                                               --------         --------

Net cash provided by financing activities                                       10,911           28,911
                                                                               --------         --------

Effect of exchange rate changes on cash                                            (30)             269
                                                                               --------         --------

Net increase in cash                                                             9,161           27,581
Cash at beginning of period                                                     17,560           35,505
                                                                               --------         --------

Cash at end of period                                                          $26,721          $63,086
                                                                               ========         ========

</TABLE> 

                                       5
<PAGE>
 
                                 CBT GROUP PLC

          NOTES TO CONDENSED CONSOLIDATED FINANCIAL STATEMENTS


NOTE 1  INTERIM CONSOLIDATED FINANCIAL STATEMENTS

 These interim unaudited condensed and consolidated financial statements have
 been prepared in accordance with generally accepted accounting principles for
 interim financial information and with the instructions to Form 10-Q.
 Accordingly, they do not include all the information and footnotes required by
 generally accepted accounting principles for complete financial statements. The
 accompanying interim financial statements should be read in conjunction with
 the financial statements and related notes included in the Company's Annual
 Report to Shareholders (Form 10-K) for the year ended December 31, 1997. In the
 opinion of management, all adjustments (consisting of normal recurring
 accruals), considered necessary for a fair presentation of financial position,
 results of operations and cash flows at the dates and for the periods presented
 have been included. The results of operations for the periods presented are not
 necessarily indicative of the results expected for the full financial year or
 for any future period.

NOTE 2  ACQUISITION OF THE FOREFRONT GROUP, INC.

 On May 29, 1998, CBT Group PLC ("CBT," or the "Company") completed the
 acquisition of The ForeFront Group, Inc ("ForeFront"). The Company issued
 approximately 2.2 million ADSs in connection with the acquisition and assumed
 options, warrants and other rights to acquire ForeFront common stock that can
 be exercised for approximately 1.0 million ADSs. The transaction is being
 accounted for as a "pooling of interests" in accordance with U.S. generally
 accepted accounting principles.

 Reconciliations of revenue and earnings previously reported by CBT, based on 
 CBT's separate results before restating for the ForeFront pooling, to the 
 combined amounts currently presented in the condensed financial statements and 
 notes to the condensed financial statements are as follows:

<TABLE> 
<CAPTION> 
                 ---------------------------------------------------------------
                 Three Months Ended                  Nine Months Ended
                 ---------------------------------------------------------------
                 September 30, 1997                  September 30, 1997
                 ---------------------------------------------------------------
                 CBT      ForeFront   Revised      CBT     ForeFront    Revised
                 ---------------------------------------------------------------
                    (dollars in thousands)           (dollars in thousands) 
--------------------------------------------------------------------------------
<S>            <C>         <C>        <C>        <C>        <C>         <C> 
Revenue        $30,412     $4,724     $35,136    $78,576    $13,042     $91,618
--------------------------------------------------------------------------------
Net Income      $5,906    $(1,172)     $4,734    $13,469    $(4,965)     $8,504
--------------------------------------------------------------------------------
</TABLE> 
NOTE 3  SHARE SPLIT

 On March 9, 1998 the Company effected a two-for-one split of its issued and
 outstanding ADSs.  Subsequent thereto, the Company's shareholders approved a
 proposal at the Company's 1998 Annual General Meeting to subdivide each of the
 Ordinary Shares of IR37.5p into four Ordinary Shares of IR9.375p (the "Ordinary
 Share Split"). As a consequence of the Ordinary Share Split, effective May 22,
 1998 each ADS represents and is exchangeable for one Ordinary Share (the "Ratio
 Change"). Aside from the Ratio Change, the Ordinary Share Split had no effect
 on the ADSs and had no effect on the number of ADSs outstanding.

NOTE 4  NEW ACCOUNTING STANDARDS

 The Company adopted Statement of Financial Accounting Standard (SFAS) No. 130,
 "Reporting Comprehensive Income" as of January 1, 1998. SFAS No. 130 requires
 disclosure of total non-stockholder changes in equity in interim periods and
 additional disclosures of the components of non-stockholder changes in equity
 on an annual basis. Total non-stockholder changes in equity include all changes
 in equity during a period except those resulting from investments by and
 distribution to stockholders. The Company has restated information for all
 prior periods reported below to conform to this standard.

                                       6
<PAGE>
 
The Company's total comprehensive earnings were as follows:

<TABLE>
<CAPTION>
                                                              Nine months ended
                                                                September 30,
                                                            1997            1998
                                                            ----            ----
      (dollars in thousands)                             (Unaudited)     (Unaudited)
     <S>                                                 <C>             <C> 
      Net Income                                           $8,504         $14,318
      Foreign Currency Translation Gains                       15             370
                                                               --             ---
 
      Total Comprehensive Income                            8,519          14,688
                                                            =====          ======
</TABLE>
                                                                                

NOTE 5  COMPUTATION OF NET INCOME PER SHARE

  The Company has adopted Statement of Financial Accounting Standards (SFAS)
  No. 128. This statement requires the presentation of basic and diluted net
  income per share. Basic net income per share is computed using the weighted
  average number of ordinary shares outstanding during the period. Diluted net
  income per share is computed using the weighted average number of ordinary and
  dilutive ordinary equivalent shares outstanding during the period. Dilutive
  ordinary equivalent shares outstanding include stock options, warrants and
  exchangeable shares. The Company has restated all prior period per share data
  presented as required by SFAS No. 128. Restated numbers as computed using the
  diluted method under SFAS No. 128 approximate those computed using the
  previous method as defined in Accounting Principals Board Opinion No. 15.


NOTE 6  COMMITMENTS AND CONTINGENCIES

  See Legal Proceedings in Part II, Item 1 and "Management's Discussion and
  Analysis of Financial Condition and Results of Operations" in Part I, Item 2
  herein.


                                       7
<PAGE>
 
                                   SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, Registrant
has duly caused this report to be signed on its behalf by the undersigned
thereunto duly authorized.

                                 CBT GROUP PLC

Date:  April 6, 1999              By:  /s/ William G. McCabe
                                       -----------------------
                                       Mr. William G. McCabe
                                       Chairman of the Board         



Date:  April 6, 1999              By:  /s/ Gregory M. Priest
                                       ---------------------
                                       Mr. Gregory M. Priest
                                       Chief Executive Officer and President



                                       8