nearly one in five teachers has been the victim of cyber-bullying, with pupils topping the list of perpetrators.
A joint internet survey, by the Teacher Support Network and the Association of Teachers and Lecturers, found that one in 10 had been bullied on websites such as YouTube, MySpace and RateMyTeachers; nearly half had been harassed by email; and almost 40 per cent had received silent phone calls.
Pupils were responsible for over a third of incidents. Seventeen per cent of teachers had taken sick leave as a result.
"Many think poking fun at teachers is harmless, but it undermines confidence and can lead to fear of going into school," said Patrick Nash, TSN chief executive.
Only 9 per cent of teachers were aware their school had a cyber-bullying policy, the study found.
Chris Keates, general secretary of teachers' union NASUWT, said: "It is still not taken seriously enough. We are talking about peoples' lives, health and careers."
The findings follow concern about the abuse of video-sharing websites. Last year, unions campaigned to have upsetting footage of teachers and schools removed from YouTube. Now, schools in three-quarters of English cities are represented on the site without their knowledge. One recent clip showed a pupil smashing a school window. There have been similar cases in Italy and Canada.
Paul Hawkins, deputy head of the Chafford school in Essex, said monitoring had become a must. "Our technicians look at YouTube and other chatrooms regularly," he said. "The beast keeps getting bigger. Search for practically any school and you'll find something concerning."
One worry is that even if teachers are spared, footage may denigrate the school. Videos of drunk pupils, low-level disruption and fist fights are often listed under the school's name or clearly show pupils in uniform.
ATL and TSN recommend that schools develop a policy and report all incidents to the sites.
Ken McAdam, of ATL, said: "We have seen cases where teachers have reported videos but the school has done nothing because they don't have guidelines, which is deeply distressing."