By Gary Eason
BBC News, at the ATL conference in Torquay
Teachers are warning parents they need to be more aware about the potential misuse of the internet and mobile phones by their children.
Mobile phones are being used to bully teachers and pupils
A survey of Association of Teachers and Lecturers members says more than half know of pupils being "cyber bullied" and 16% have been victims themselves.
Union leaders said schools should use the available sanctions, such as confiscating phones, more consistently.
They said pupils knew how to get hold of teachers' e-mails and phone numbers.
Speaking to reporters at the union's annual conference, in Torquay, union general secretary Mary Bousted said: "The internet and mobile phones are here to stay.
"What schools have got to have are very robust policies in place, which they enact.
"If a student is given a teacher's e-mail address or mobile phone number they must know that's a very valuable piece of information and they mustn't abuse it."
She said often children did things simply because they could, but when the consequences were explained to them they were very shamefaced.
But most cyber bullying happened outside school hours, so it was difficult for schools to police, she added.
Matt Whittaker from Burleigh College, Leicestershire, said: "An area I am very aware of, due to it affecting my own children, is pornography on phones and the ease of file sharing.
"My 11-year-old girl watches hard-core porn in school playgrounds and I can't do anything about it. This is child abuse.
"Parents need to be made aware of what their kids' videophones are being used for, because it's not for talking to each other on."
In England, the government has said it wants to see more online reporting to parents by schools.
Dr Bousted said it seemed ministers felt parents needed continual engagement with their children's schools.
"What we are saying to the government is this is a complex issue, because it's not just students who can behave inappropriately through the internet it's parents as well," she said.
"I can well envisage occasions where parents send abusive e-mails to teachers because Johnny's got an E in his history essay."
A Department for Children, Schools and Families spokeswoman said schools, like any other employer, must protect their staff from any form of harassment.
"We now have an advanced approach to cyberbullying, thanks in no small part to cooperation with the industry, teaching unions and charities.
"This guidance gives teachers and parents all the knowledge they need to tackle the problem effectively in schools."