Within hours of the conference opening the following day, moderates and hard-liners had overwhelmingly backed a work-to-rule, in protest against the Government's controversial plans to introduce performance-related pay.
The action, which significantly has the backing of the union leadership, begins what general secretary Doug McAvoy promised would be a long campaign to force ministers to scrap or modify the new salaries scheme.
The union's 200,000 members will vote on the work-to-rule, which could lead to them refusing to take part in after-school clubs, evening meetings and other non-contractual activities.
The NUT membership will also be asked to consider supporting a one-day strike after moderates failed to quash a conference motion in support of a national stoppage - the first for 31 years. However, it seemed unlikely to win grassroots support after Mr Mc-Avoy refused to back it, insisting it would fail to deflect the Government and would alienate parents.
Soon afterwards the schools minister Estelle Morris, making her first platform appearance at an NUT conference, was subjected to a staged walk-out by up to 400 delegates and heckled by other hard-line opponents of the Government's pay scheme.
The temperature was further raised on Monday when the chief inspector for schools, Chris Woodhead, went on Radio 4's Today programme to accuse the union of using children as "pawns in a game" in an attemt to force the Government to back down. He dismissed claims by NUT delegates that teachers would inevitably pass on their stress to pupils.
The chief inspector's remarks earned a rebuke from Nigel de Gruchy, general secretary of the National Association of Schoolmasters Union of Women Teachers. Mr de Gruchy, whose own union is reluctantly backing the scheme, claimed Mr Woodhead's intervention would simply increase staffroom support for the NUT's anti-PRP stance.
The NASUWT opened its own conference in Llandudno with a sharp rebuke of its own. Its president, Martin Johnson, singled out prime minister Tony Blair, for encouraging creeping academic selection and giving preferential funding to specialist and beacon schools. He accused Mr Blair of being "a bourgeois prime minister", who had "absolutely no understanding of how ordinary schools work".
But the union warmly received an announcement by the Education Secretary David Blunkett of an additional pound;47 million to be spent on building "sin bins" to enable unruly pupils to be taught separately as an alternative to exclusion. The investment is central to ministers' strategy to cut exclusions by a third by 2002.
If the big classroom unions were making most of the news over Easter, the media-savvy leader of the National Association of Head Teachers was ensured publicity with an attack on the makers of Pokemon cards. David Hart accused the company of using "irresponsible" sales techniques to whip up the latest craze among primary children.
Mr Hart said the cards, which feature more than 100 different fantasy monsters, have led to bullying and fights among pupils.