More than one in 10 headteachers has been attacked by a parent of a pupil at their school, according to figures released today.
School leaders have been punched, kicked, spat on, head-butted, bitten, attacked with chairs and tables and sexually assaulted, the National Association of Head Teachers (NAHT) said.
In a survey, almost 75 per cent of those quizzed said they had suffered verbal abuse or threats from a parent in the last five years.
Some 20 per cent have been victimised on a social networking site and more than 68 per cent said parents' behaviour towards teachers has worsened over time.
Headteachers polled said that in some cases parents have turned up at school drunk or high on drugs.
Russell Hobby, general secretary of the NAHT, said: "Policy-makers need to be aware that school leaders are not faceless bureaucrats who must be exposed to the public to help them 'shape up'.
"They live and work in the cities, towns and villages that they serve. They meet parents daily inside and outside school, and they are instantly recognisable.
"Alone, in the school car park after a late governors' meeting, parental pressure can take on a new meaning.
"The vast majority of families are a pleasure to work with but not all. Emotions run high when children are involved. School leaders often have to make difficult decisions about discipline, exclusions, holidays and the distribution of limited budgets.
"Many come under unacceptable pressure designed to effect undue influence on them. All are dedicated to doing what is best for the children in their care. Some pay a high personal cost for this dedication."
The survey was conducted by the NAHT this month, with almost 1,400 members taking part.
A Department for Education spokesman said: "We want to give parents a choice of good schools in their area. But this of course does not in any way excuse aggressive behaviour towards school staff by a minority of parents.
"Violence against staff by parents or pupils is completely unacceptable. A physical assault against a teacher is a criminal offence and we support schools in working with the police to take firm action where needed."