Pupils are using their mobile phones to call their parents during lessons to complain about their teachers, heads say.

Unaware of the situation, head teachers were then finding themselves face to face with angry parents, general secretary of the National Association of Heads Teachers, David Hart, told delegates at the union's annual conference in Harrogate.

There are too many 'parents from hell' who delight in making the lives of heads and their staffs as difficult as possible

David Hart

It is thought about 350,000 pupils under the age of 16 have a mobile phone.

But despite best efforts on the part of head teachers to ban them, they were still widely used, Mr Hart said.

And the trend of text-messaging has meant children can contact the outside world surreptitiously.

'Another weapon'

Mobile phones gave pupils another opportunity to register complaints against teachers and many of those complaints could be malicious or ill-founded, Mr Hart said.

"Mobiles give pupils another weapon in their armoury to make life difficult for teachers," he said.

Mr Hart said a secondary head teacher at a school in north London had had irate parents knocking at the school door to remonstrate with her before she had been told what had happened.

"The simple basic fact is that there are too many 'parents from hell' that delight in making the lives of heads and their staffs as difficult as possible," Mr Hart told delegates.

He called on the government to remove the doubt surrounding a head teacher's power to exclude a pupil because of the behaviour of his or her parents.

"In extreme cases, where the relationship between school and parents has broken down, because of outrageous behaviour by parents, heads should be given that right, as a protection for them and their staffs," he said.

Bad parenting

Too many parents were parenting badly, too many parents were over-eager to challenge heads and their staffs, he told the conference.

Mr Hart accused the government of dealing with the issue of violence towards public servants in a "piecemeal" manner.

"There is not a comprehensive and coherent plan to deal with all aspects of the exclusion process," he said.

While the NAHT did not support the Conservative party's route of absolute exclusions, the Labour government had not got it right yet, he added.