The NUT had offered him just 10 minutes, barely enough time to quieten the hecklers. But this is about more than wounded pride. After all, the education secretary's bruiser skills are legendary.
Mr Clarke was reinforcing his decision to isolate the NUT for refusing to join the Association of Teachers & Lecturers and the NASUWT in signing an agreement with the government on teacher workload.
That deal aimed to cut teachers' term-time working hours from over 50 hours a week to 45, by employing more support staff. In return, those signing accepted that teaching assistants could occasionally teach classes.
and that 'class sizes of 60' will result.
But the government can point to increasing numbers of teachers and assistants every year since 1998 and lower class sizes.
Indeed, the union's critics believe the real reason NUT general secretary Doug McAvoy would not sign is because he could not sell the agreement to his left-dominated union executive.
And Mr McAvoy is increasingly isolated. This time last year, union unity was in the air, after the pro-merger Eamonn O'Kane became general secretary of the NASUWT. Mr McAvoy thought unity would isolate his militants. But Mr O'Kane alienated his own activists by jumping the gun, so unity is no longer a serious prospect.
While snubbing the NUT, Mr Clarke will address the Secondary Heads Association, which kicks the conference season off in Birmingham later this month, and the NASUWT in Bournemouth after Easter. School standards minister David Miliband will speak at the ATL in Blackpool and junior minister Stephen Twigg will address the National Association of Head Teachers in York in early May.
Before their conference ATL members must choose a replacement for retired general secretary Peter Smith, the government's most supportive union leader. Three candidates hope to succeed him. The leadership's preferred successor is Dr Mary Bousted, head of Kingston University school of education. But she faces a strong challenge from Mr Smith's deputy Gerald Imison, who helped negotiate the workload deal.
The outsider is Hank Roberts, whose commitment to teacher unity is such
that he has joined all three main unions, and whose election would spell trouble for the government, as he opposes the workload deal.
Union opposition to this year's inflation-matching pay deal may have been fairly muted, but anger at lower funding increases for many south-east councils
as part of this year's local government settlement could explode at the SHA conference. Croydon heads have threatened a four-day week, and heads in other areas expect to reduce their workforce.
The NUT will also hear calls for the axing of primary school tests and league tables to go. All the conferences will urge ministers to ease tough national curriculum test targets. Even Ofsted, once the union bugbear, has questioned whether the 2004 goals can be met. But such calls will be resisted by ministers, who attribute recent progress partly to targets and tests.
It may be business as usual in some respects. But Mr Clarke's boycott has set the tone for a grumpy and divisive Easter.
Special adviser (1997-2001) to former education secretary David Blunkett