Teachers and heads stand together in strike threat

Incoming government will face walkouts in protest at class sizes and long working hours, as well as a boycott of national tests

Teachers threw down the gauntlet to an incoming government yesterday by voting in favour of national strike action for a 35-hour week. Delegates at the National Union of Teachers' annual conference in Liverpool unanimously backed a motion calling for the action to bring about smaller class sizes and a reduction in their workload.

It is one of a series of moves being planned by the NUT that will put it on a collision course with whichever party wins the general election. The union, in conjunction with the National Association of Head Teachers, is also balloting its members on boycotting national curriculum tests for 11-year-olds – due to start on 10 May, four days after the anticipated election date.

Delegates yesterday gave a standing ovation to Mick Brookes, general secretary of the NAHT, when he addressed the conference and told them: "If they're [the Government] not going to change the system, we should change the system for them."

Tomorrow, delegates also debate an emergency motion threatening strike action in the event of a public sector pay freeze or cuts in spending.

Research by the TUC shows teachers worked more unpaid overtime – 18.7 hours a week on average – than other public sector employees. Much of the extra work is a result of new government initiatives and targets being set for individual pupils, delegates said.

Speaking at the conference yesterday, Sue McMahon, from Calderdale, West Yorkshire, said: "The more we do, the more we're expected to do. Teachers spend their holidays planning new schemes of work, evenings marking books and weekends marking and looking at target data." She added: "I'm sick and tired of the amateurish interference from the professional politicians. We may end up having a barney with the next government if we as professionals aren't treated like professionals."

The motion called on the union to mount a campaign for a 35-hour week, limits on class sizes (no more than 20 pupils a class by 2020) and an end to "a culture that believes teaching is improved by making ever more demands on teachers in a more and more bullying way".

In his address to the conference on the proposed test boycott – the first time a head teachers' leader has addressed the conference, Mr Brookes said: "Let there be no doubt this is a legal and valid dispute." He said he expected up to 7,000 of England's schools would have to cancel the tests if the ballot result produced a two-thirds majority for a boycott, as had happened in an earlier survey. The unions oppose the tests, which are taken by 600,000 pupils in maths and English, because their results are used to compile national league tables, forcing teachers to teach to the test to ensure they perform well in the tables.

"[The Schools Secretary, Ed Balls] has allowed a system to continue which humiliates and demeans the work of those schools in the toughest places, where children are at times hard to teach and where parents are at times hard to reach," Mr Brookes added.

Vernon Coaker, the Schools minister, said: "We don't think that a boycott would be in the best interests, and we urge heads and teachers to use their professional judgement and keep talking to the Government about the future of testing." The Government has said it would be prepared to replace the tests in future with teacher assessments if they are shown to be as "robust" as externally marked tests.