In March, tens of thousands of pupils left lessons to protest against the war

During the Iraq war, thousands of pupils walked out of school to demonstrate against the conflict.

But David Hart, general secretary of the National Association of Head Teachers, says that pupil protestors face punishment for missing lessons.

This tougher message is backed by the Department for Education and Skills.

The arrival of Mr Bush this week has raised the prospect of a repeat of the involvement of school pupils earlier this year in demonstrations held to stop the war in Iraq.

'Loud and clear message'

Last March, an estimated 10,000 pupils walked out of lessons to take part in anti-war protests, including demonstrations in Parliament Square and outside Downing Street.

Mr Hart has played down concerns that there will be large numbers of pupils taking part in protests this week - but he says that any pupils who do attend rallies during school hours will face punishment as unauthorised absences.

"They will have got the message out loud and clear to pupils that failing to attend school because they want to go on demonstrations against George Bush is simply unacceptable. It will be treated as truancy and schools' disciplinary sanctions will apply.

"Either they will be given a detention or a fixed-term exclusion. There can be no doubt whatsoever that it is not appropriate for any pupil to bunk off school in order to demonstrate against George Bush during school hours.

Parents

"If they want to demonstrate, they have every right to do so outside school hours," said Mr Hart.

Parents were also told that if they allowed their children to attend protests, rather than school, it would be "treated in exactly the same way as if they parent took them away for a day's jolly".

Even if head teachers were sympathetic to the protests, Mr Hart said that they would not condone pupils' absences.

The Department for Education and Skills supported this view that pupils should not miss lessons without permission.

"While we fully respect young people's right to protest, this should be done outside of school hours. During the school day we expect pupils to be in school. If a pupil is out of school without permission the absence is, of course, unauthorised and the parents should be informed," said a Department for Education and Skills spokesperson.