Image copyright Thinkstock Image caption Teachers can be "traumatised" by online smears, says teachers' union

Online social media is being misused to insult, intimidate and smear staff in schools, the conference of the NASUWT teachers' union has heard.

More than one in five teachers had "adverse comments" written about them on websites, according to a survey of 7,500 of the union's members.

A quarter of these insults were from parents - and there were attacks from pupils as young as seven.

Teachers are often "devastated" by the abuse, says union leader Chris Keates.

These insults, posted in places such as social networking websites, are attacks on teachers' "appearance, competence or sexuality", according to the NASUWT survey.

More than a quarter included videos or pictures taken without the consent of the teacher.

Some have lost their confidence to teach once they see foul and personal remarks made Chris Keates, NASUWT leader

Teachers had faced racist insults, malicious allegations of hitting pupils, accusations of swearing at pupils and "inappropriate behaviour", says the teachers' union. There had also been threats made against teachers.

Pupils were responsible for most of the online abuse - but 27% was believed to be from parents and 9% was from parents and pupils together.

But fewer than half of these incidents were reported to the school or the police - with some teachers "too embarrassed".

Where teachers did report such attacks, the survey claimed head teachers took no action in 40% of cases where the insults were from pupils and in 55% of cases where they were believed to be from parents.

"Teachers are often devastated by the vile nature of the abuse they are suffering," said Ms Keates, the union's general secretary.

"Teachers are often traumatised by the attacks made on them through social media.

"Some have lost their confidence to teach once they see foul and personal remarks made by pupils in their classes and have left the profession.

"Others have been so disturbed by the comments that their health has been affected."

She called for schools to have clearer sanctions against parents and pupils who carry out such online abuse and for a better system for removing offensive material from websites.