As many as 300,000 11-year-olds will find their national curriculum tests cancelled this morning.
The estimate of the amount of disruption caused by a boycott of the tests – in maths and English – increased yesterday. Christine Blower, general secretary of the National Union of Teachers, said that the number of schools backing the boycott ranged from 30 per cent to 75 per cent from local authority to local authority. Overall, about half of the 17,000 schools due to sit the tests are set to abandon them.
Ms Blower added that, if no agreement could be reached on reviewing the tests and scrapping exam league tables derived from them, the boycott could be repeated next year.
"We would have to consider that," she said. "The purpose of the boycott is to get rid of the SATs (national curriculum tests). If we had a different series of tests and a categorical agreement there would be no league tables, then obviously that would be different."
Both Labour and the Conservatives are committed to the test going ahead. However, teachers' leaders are pinning their hopes on Liberal Democrat involvement in the new government because the party spoke out against the tests and exam league tables during the election campaign.
The NUT – along with the National Association of Head Teachers – has voted in favour of boycotting the tests because they believe the importance placed on them – with performance tables based on their results – has forced schools to teach to the tests at the expense of the broader curriculum.
It will mean headteachers refuse to distribute the test papers to pupils but otherwise remain at work.
Teachers' leaders believe the rise in the numbers of heads boycotting the tests could be down their feeling less fearful of the the threat of reprisals as a result of the stalemate over the formation of the new government.
The Schools Secretary Ed Balls had urged school governors to consider sending heads home if they refused to administer the tests – and said they should consider appointing another "competent" adult to ensure they went ahead.
However, the National Governors' Association – which represents school governing bodies – warned of the dangers inherent in such action.
"The NGA would not advise any governing body to go ahead without considering how they could fund any legal dispute which arose from this request," it says. "The unions are highly likely to challenge any employer who requests an employee be sent home (who is only carrying out part of their duties as a result of industrial action)."
Meanwhile, at an anti-SATs rally in London's Jubilee Gardens yesterday, children's authors revealed they would be going into schools to read poetry and tell stories to provide pupils with an alternative to the SATs.
The author Alan Gibbons said at the rally: "We will be conducting poetry sessions, reading books and doing story-telling activities – trying to show an alternative approach to SATs."
More than 90 children's authors and illustrators signed an open letter to the Government warning that the tests were switching pupils off reading because they concentrated on learning excerpts from books for the tests rather than reading the whole story.
Ms Blower told the rally: "We are standing up and saying we must get rid of the SATs and the league tables. Let's make sure that every child has a great year unencumbered by ridiculous tests and make schools a SATs-free zone."
The first test – English reading – is due to take place today and will be followed by three more days of tests. These include a writing test and two maths tests, one concentrating on mental arithmetic.