A workshop on bullying at the Association of Teachers and Lecturers (ATL) conference in Torquay this week heard of incidents of primary pupils and staff being victimised via modern technology.
Liz Coston, a south London primary teacher, said she was aware of pupils as young as eight or nine sending bullying messages to other pupils by instant messaging or email.
Her school had temporarily excluded an 11-year-old who brought violent and intimidating video footage to school on his mobile phone to show other pupils.
Six other primary teachers at the conference said their pupils had suffered cyber-bullying, most often through threatening messages in internet chatrooms. Three primary teachers had suffered cyber-bullying and said it had affected their self-confidence, caused them illness, and made them scared outside work.
Mrs Coston said pupils were able to send such messages because they were spending increasing amounts of unsupervised time on the internet at home. "Parents use the internet like a babysitter," she said.
There were calls at the conference for a total ban on mobile phones in schools. Jim Knight, schools minister, has said the Government does not plan to impose a blanket ban, but will leave the decision to individual schools. But in Torquay he faced renewed pressure from teachers who believe mobile phones have no place in schools.