Launching a new poster and guide to help heads defend their staff from assault, education minister Stephen Twigg agreed with a questioner that excluding a pupil might be necessary "in extreme circumstances", where the parents' attitude had caused a breadown in relations with the school. His remark was welcomed by the National Association of Head Teachers, which demanded the power at its conference last month.
But it was condemned by heads attending a behaviour summit hosted by Prime Minister Tony Blair on the same day. Rosemary Roscoe, head of Trinity school, Newbury, Berkshire, said: "For goodness sake, schools have to change children, not punish them for the behaviour of their parents."
And Doug McAvoy, general secretary of the National Union of Teachers, said he would prefer to see the use of orders banning parents from school premises.
A spokeswoman for the Department for Education and Skills said it would look at any policy that would help schools but no new initiative was planned.
Mr Twigg unveiled the poster at his former school, Southgate in Cockfosters, north London. It says: "We welcome visitors to our school."
But adds: "If you threaten or assault anyone in the school, or persist in abusive behaviour, you will be removed from the premises and may be prosecuted."
The guide explains that parents who assault a teacher could face a pound;5,000 fine and up to six months' imprisonment.
Margaret Morrissey, spokeswoman of the National Confederation of Parent Teacher Associations, said it was sad that ministers had missed an opportunity to discuss the problem with "positive" parents, governors and unions.
"It's going to take a lot more than a few posters and warnings to solve," she added.