Teachers in England are being alerted to guidelines on how they can tackle homophobic bullying.
Most gay youngsters say bullying affects their schoolwork
Pupils might be bullied if they are gay or are thought to be - or if their parents are - and teachers may also be targeted, the guidance says.
Drawn up for ministers by gay rights groups, it was first published last autumn.
Teachers' leaders say bullying related to prejudice is a significant problem, and they welcome the information.
Schools have a legal duty under the Education and Inspections Act 2006 to ensure homophobic bullying is dealt with - along with other types of bullying.
The guidelines on homophobic bullying say victims may miss school and have low self-esteem, and be at increased risk of self-harm and suicidal thoughts.
Seven out of 10 young lesbian and gay people say homophobic bullying affects their school work, they say.
Teachers are given guidance on how to recognise homophobic bullying and examples of unacceptable language such as "You're such a gay boy!" or "Those trainers are so gay".
The advice says homophobic bullying can take place in primary schools, even though pupils might not know the meaning of some of the words they use.
And children whose parents, carers or relatives are gay might be targeted by bullies.
Schools are told their response to homophobic bullying - as with other forms - should be "swift, proportionate, discreet, influential and effective".
They are given a step-by-step guide to tackling verbal abuse, beginning with all pupils being told that homophobic language will not be tolerated and increasing to pupils being taken out of the classroom for talks on their attitudes and then parents being called in.
The campaign groups Stonewall and Each drew up the guidelines for the government.
Stonewall chief executive Ben Summerskill said: "It is very encouraging the government has recognised this form of bullying as a serious problem, which can have such a damaging effect on children.
"When writing this guidance, we ensured it was specifically designed to give teachers more confidence to confront the problem.
"This is a significant step forward in our campaign to tackle homophobic bullying."
Schools Secretary Ed Balls said: "Even casual use of homophobic language in schools can create an atmosphere that isolates young people
and can be the forerunner of more serious forms of bullying".
The general secretary of the NASUWT teachers' union, Chris Keates, said: "This is a vital initiative which puts homophobia at the heart of schools' anti-bullying strategies.
“Prejudice related bullying has become an increasingly significant problem in schools, colleges and the wider society. Schools need a clear plan of action within a national framework to tackle it."
Many teachers had reported being victims of homophobic bullying, she said.
“The NASUWT has had several cases this year where teachers have reported suffering homophobic bullying only to be told by senior managers that it is not in their own or the school's interests to take the matter further."