Teachers should caution students that engaging in "sexting" and revenge porn could result in a criminal conviction, according to new guidance.

While making their pupils aware that such behaviour is not a "normal part of relationships", teachers should also deliver "reassurance messages" for teenagers who have already engaged in these activities, according to the document compiled by the Home Office's crime prevention panel and the NSPCC children's charity (see www.tesconnect.comNSPCCguide).

The guidance, shared exclusively with TES, also advises teachers on how to dissuade young people from cyberbullying, trolling and hacking. It urges staff to tell pupils that their actions will "follow them offline".

For 13- to 19-year-old students, the guidance says that teachers should be clear that it is "not OK" to hurt or upset others online, steal someone's identity or share inappropriate images of young people aged under 18.

The report says "anecdotal evidence" shows that young people "consider sharing selfies and sexting to be a normal part of relationships". Because of this, it adds, teachers should make clear that it is illegal to take and share indecent photos of under-18s.

Without asking "leading questions" and being judgemental about young people's online behaviour, teachers should warn them that what they post on social media could affect their future employment prospects, the report says.

"Online abuse can be a devastating experience," said crime prevention minister Lynne Featherstone. "It is important that young people are well informed about how their behaviour could impact others and affect their own future prospects."

Emily Cherry, head of participation at the NSPCC, said: "This resource will give teachers and youth workers a way of ensuring they have the best advice possible to prevent young people from getting caught up in online crime."