Teenagers believe it is acceptable to call classmates “gay” if they walk differently or do not want to hang out with friends after school, despite receiving lessons on the importance of inclusion, according to new research.

“Gay” is used as a general insult by children who know that homophobic insults are wrong, because they believe that the word has two distinct meanings, academics have found.

The researchers, from the University of London’s Institute of Education and the University of New South Wales in Australia, interviewed staff and students at three state secondary schools in South London. In each school, homophobia had been addressed by staff and firm anti-bullying policies put in place, but homophobic abuse still continued.

“Equal opportunities should be addressed in schools, and I think that homophobia is one that is often left out,” a member of senior management at one school said. “You need.to give it the same kind of.support and value as you would for racism or sexism.”

Students at all schools had a fairly clear understanding of what homophobia was. One boy described it as “cussing someone, because they are gay” or because gay people “are different to you”.

And they understood that homophobia was a form of prejudice. One Year 10 boy said: “People have prejudices against people who are homosexual or lesbian, simply for the fact they don’t think it’s right.” Another said: “It’s one of the worst possible ways to insult someone.”

However, such arguments against homophobia were tempered by specific concerns about gay people. For example, several girls said that they preferred gay men to lesbians, because a lesbian “might come on to you”. Gay men, by contrast, were “not going to start touching you, as they fancy men”.

The findings come after the publication last week of new guidance on sex education in England. This calls for a greater understanding of same-sex relationships, and advises teachers to refer to “partners” rather than “boyfriend” or “girlfriend” to help incorporate same-sex relationships into classroom discussions.

According to the new research, many students draw a clear distinction between homophobic bullying and comments made in a friendlier context. “It’s, like, two different meanings, the way we use it,” one Year 10 boy said. His classmate added: “Like, the teacher saying you’ve got detention and you say, `That’s gay.’ ”

A Year 9 girl echoed this, saying that “you’re gay” was a reasonable comment to make “if you’re a bit odd [or] if you walk a bit different”.

“I think people.don’t take it offensively,” added one of her classmates. “I use it when I’m mucking about with someone.”

The Year 9 boys also drew a distinction between homophobia and casual insults. One boy said: “They go, `Oh, do you want to come here after school?’ and you go, `No’, then they say, `You’re gay.’ ”

“I’m an idiot, then you call me `gay’,” another boy said. A third added: “If it takes too long to get somewhere, then that’s gay.”

This distinction was noted by some of the teachers interviewed. One said that students divided comments about other people’s sexuality into “Yeah, I meant to be offensive” or “I’m talking to my mates, Sir. It doesn’t matter”.

Several teachers had also considered whether to ban students from using phrases such as “you’re gay” in school. However, most had decided that it would be better to encourage discussion among students about the potential harm caused by such words.

A recent survey by gay rights charity Stonewall shows that 85 per cent of students in the UK are not taught about the physical or biological aspects of same-sex relationships at school. More than half of gay and bisexual students have experienced bullying at school.

Sue Sanders, co-chair of the lesbian, gay, bisexual and trangender teachers’ organisation Schools Out, said: “If I were to say, `Oh, that’s so Jewish’ or `that’s so Muslim’ or `that’s so blind or deaf’, how would you feel about that?

“Language needs to be used carefully. Using the word `gay’ in that way adds to and colludes with homophobia. Saying that you’re not being homophobic is not taking responsibility for putting poison into the air.”

Stonewall and Schools Out have shared resources to support teachers dealing with homophobic language and bullying at school.