Cases of pupils bullying teachers are not always reported
Many teachers are being bullied and harassed by pupils, but school heads are concealing the problem, says the National Association of Head Teachers.
When the NASUWT teachers' union asked its members about the issue, many said they had been taunted, abused or physically attacked by their pupils.
And the NAHT union said its members feared reporting ill-treatment would reflect badly on their school.
Head teachers' leaders insist they take their responsibilities very seriously.
Ministers say heads have a duty to report cases of teachers being bullied.
They said new powers make it easier for schools to tackle the problem.
HAVE YOUR SAY
How about letting the teacher discipline the children appropriately as some parents fail to do this basic task.
Robbie Mutton, Inverness
The NAHT's general secretary, Mick Brookes, told BBC Breakfast: "I think we're quite right in asserting the under-reporting of these sorts of incidents because it's not the sort of thing that schools, and even teachers, will want to be shouting from the rooftops."
One teacher, who did not want to be named, said: "There have been times when the bell's gone for the end of that lesson, and I've got out of there as quickly as possible because you're just so nervous.
"I've been punched a number of times, I've had aerosols sprayed into my face, I've had my mobile phone stolen and texts sent out to my friends.
"I've been intimidated by a group of year 11 pupils, I've had a torrent of abuse and, on one occasion, I've even been asked to hide in an office because a child had come in with a knife, looking for me."
John Dunford of the Association of School and College Leaders said: "Head teachers take their responsibility to protect staff very seriously. No one, teacher or student, deserves to be bullied, but the issue is not as clear cut as it may seem.
"There is a fine line between rowdy behaviour by groups of students and direct bullying of teachers. In the case of bullying, heads have a duty to protect staff but in other instances the more effective response may be to help struggling teachers develop better classroom management techniques.
"This is where peer observation to reflect on, and improve, classroom management can be effective."
Children's Minster Kevin Brennan said: "Any incident of bullying or assault on teachers is unacceptable. Standards of behaviour in all schools have been steadily improving according to Ofsted and although assaults on teachers are rare, as a former teacher I know that one assault is one too many.
"That is why we have given teachers and Heads the statutory powers they asked for to enforce discipline in schools and we fully support them in using them."