Head teachers say a rise in parent violence in schools can be explained by the "rights culture" and a lack of respect for authority figures such as teachers.

And a culture of aggression, which spills over into the playground, is fuelled by confrontational television chat shows, say heads.

According to the National Association of Head Teachers, meeting for its annual conference in Harrogate, up to two heads are assaulted by parents every week.

The union says its caseload of parent violence related cases has doubled over the past year.

"We need to be as keen on parental responsibilities as on parental rights," said the union's general secretary, David Hart.

Think of how many chat shows whip people up to violence and get them to argue - preferably on screen. It's an appalling model to show.

Simon Marsh

Simon Marsh, head teacher of St Mary Magdalene primary school in Islington, London, said a balance must be struck.

"Society is overloaded with rights, but won't accept the responsibilities that go with them.

"For example, my right not to have my child bullied needs to be accompanied by the responsibility to see that my child doesn't bully.

"The right not to be bullied is there, but the responsibility to ensure their child doesn't bully is not there," Mr Marsh said.

Violent expression

Much of the violence towards head teachers may be explained by the fact that society has become more violent in its expression, Mr Marsh believes.

Simon Marsh: "Society is overloaded with rights"

"Think of how many chat shows whip people up to violence and get them to argue - preferably on screen. It's an appalling model to show.

"People are treating each other in a way we wouldn't have tolerated some years ago," he said.

And breaking up fights between parents was becoming an all too often task in a head teacher's day, Mr Marsh said.

The Islington head teacher, who has been scratched when breaking up a fight between parents, said ten years ago this would have been considered unusual but was now the experience of many heads.

More often than not, outbreaks of fighting - whether it be about an argument on the estate or a disagreement between children - tended to be between mothers, not fathers, he added.

'Teacher-bashing'

Mick Brookes, NAHT president from 2000 to 2001, put "teacher-bashing" as the backdrop against which violence towards heads was set.

"Senior figures continually carping about schools and what they should be doing has encourages members of the public to think less of them," Mr Brookes said.

There was also a growing disrespect for authority generally in society, he said.

"There is a sub-culture of violence in society - it's good to be hard, it's good to do someone over."

'Last resort'

Mr Hart said the belief that violence was a first and last resort was taking root.

"We have seen an increased number of people who no longer wish to argue out their grievances and use the formal complaints procedure," Mr Hart said.

"There seems to me to be an increase in the number of people taking the law into their own hands," he said.

And such behaviour was not restricted to schools but could be seen, for example, towards staff in the health service, Mr Hart added.