Head teachers say they are increasingly being abused, threatened and assaulted by parents.
Attacks and threats are growing, says the NAHT
The National Association of Head Teachers says, in January alone, five head teachers were attacked by parents, while 10 were threatened by them.
And it says threats are often also directed against other staff, school governors or head's families.
At its annual conference, in Telford this weekend, the group called for tougher action against abusive parents.
Head teacher Rachel Voss, from Norfolk, has described how she was harassed by parents after expelling their children.
She says she and her family as well as teachers and governors at her primary school in Wisbech were harassed, intimidated and threatened by the parents.
Mrs Voss was chased in her car down a busy road and her family, including her child, received telephone threats, she said.
School governors and teachers were also threatened and there were a series of incidents, such as car tyres being slashed.
Eli Frankham, 40, and his wife Vanessa both admitted harassing Mrs Voss and being abusive towards members of her staff when they were prosecuted after the incidents last year.
In September, Eli Frankham was given an 18-week sentence, while Vanessa Frankham was given community service.
At the National Association of Head Teachers (NAHT) conference, delegates said schools only reflected what was happening in society generally - with fire crews, police and hospital staff also being attacked and "road rage" common place.
They said their problems typically were associated with complaints over a child's schooling or behaviour.
But parents also waded in on behalf of their children in disputes with other pupils.
Sometimes this involved a parent waiting outside the school gate or even going into the playground and accosting a child.
Chris Harrison, who represents the association in Suffolk, said that in his county the education authority had agreed a protocol with the police on how such cases would be dealt with.
Parents were now given this - spelling out the likely consequences for them if they assaulted staff - as part of the information about schools.
NAHT general secretary David Hart said he thought every area should adopt the same sort of policy.
And he repeated his call for pupils to be expelled over the behaviour of their parents - which currently is not allowed.
"To say you can't exclude because of the parents' behaviour isn't very helpful if the relationship with the school has fundamentally broken down," he said.
"The rising level of abuse, threats and assaults by parents towards our members is totally and utterly unacceptable
"Although we are still talking about a small minority of parents, this is what is happening on the 'front line' far too frequently.
"Some parents are unwilling to pursue their complaints by using the existing procedures properly. They use violence or threatened violence as a first resort."
One ongoing case - he could not give details - involved "extreme violence" against one of his members in their own home.
Mrs Voss, who is the head teacher of the Anthony Curton Church of England Primary School in Walpole St Peter, said her experience showed how vulnerable head teachers and school governors were.
"It was a horrible experience. I felt as if my life was unravelling. I thought I might have to move away because of the threats to my family. However, a lot of good came out of this.
"We had good support from the diocese and the local authority and we pulled through with Dunkirk spirit.
"But I have since heard of people who have been through similar experiences without support and have been broken by it."
Both Labour and the Tories have made tackling indiscipline in schools an election priority.
Labour says it wants a "zero tolerance" approach to all forms of disruption including low-level bad behaviour.
The Tories says they would give heads who decide to expel unruly pupils the final say by abolishing the appeals panels that parents sometimes use to get their children reinstated.