"One of the most frequent things schools say to me is that they don't have any gay pupils," says Gavin Boyd, education equality officer for the Rainbow Project, which works to promote the health and wellbeing of gay, bisexual and non-heterosexual men in Belfast and Derry.

There's a chuckle in Boyd's voice as he relays this scarcely credible notion, but it soon gives way to the deadly serious fact that young gay and bisexual men have the highest incidence of HIV in the population. "There's a cavalier attitude, especially among young people, that you tend not to die from Aids any more, so it's seen as a manageable condition," he explains.

If young people don't have the chance to openly discuss the implications of risky behaviours, he adds, they can't make informed decisions about their sexual choices.

But the Northern Ireland curriculum makes no mention of sexual orientation, and because sex and relationships education (SRE) is not state regulated there Boyd says individual schools can deliver whatever information they choose. His service, for young people aged between 14 and 25, tries to fill the gap with practical and emotional advice and support, but it's clear that the stigma around being lesbian, gay, bisexual or transgender (LGBT) in NI in particular is enormous. The current NI commitment to review SRE for those of a minority sexual orientation will require a significant culture shift before schoolchildren of all sexualities are seen as equal in the classroom.

Achieving that equality of access to vital – sometimes lifesaving – information on sex and relationships is a basic right that should be enshrined in the national curriculum says Wes Streeting, head of education at Stonewall, the charity that campaigns for equality and justice for lesbians, gay men and bisexuals. And the fact that England's Department for Education is in the middle of a curriculum review offers a prime opportunity to do just that.

"Good practice is hard to come by at the moment. All young people, whether gay or straight, need to be aware of how to have a healthy and stable relationship," he says. "And for young people who may be struggling with their sexual orientation, it's really important that they're not the one who have to awkwardly put their hand up and ask a question. That's why it has to be delivered as a matter of course through the curriculum."

At Brook, the young people's sexual health charity, Kai Wooder, education lead for the north of England runs a weekly LGBT youth group on the Wirral. A survey of the sex education group members had received in school included comments from one young woman saying: "It was all heterosexual. Knowing that I was a lesbian meant that the sex ed lessons meant nothing to me." Another said: "I wish we'd learned about homophobia and about how to 'come out' because I didn't have a clue and school was not a good place for me."

Encouragingly, says Wooder, schools are gradually becoming "more open" to addressing LGBT pupils' needs, "but what I'd add is that teachers will do it as a separate one-to-one conversation outside the classroom. And what that does is reinforce the idea of the difference and the stigma."

Recently, her LGBT group ran a project called Love is Love for their contemporaries in local schools: all headteachers were made the offer of the group coming into class to present a session, and though not all took it up, Wooder feels it's encouraging that a few did. The project raised another issue that affects the wider population of teenagers, she explains: it's about "how we support their straight peers, because they often want to really support their LGBT friends".

Though teachers may be worried about pupils accusing them of being gay, and of the potential backlash from parents and unsympathetic school governors if they teach about sexuality and relationships in the round rather than just from a heterosexual perspective, Wooder says it is actually very easy to create an SRE lesson that is inclusive without going into detail. To achieve this however, the language used in a classroom is vitally important, and teachers need to examine their own assumptions and prejudices in advance.

"When you talk about love and relationships, instead of saying 'when a man and woman have sex' you could say 'when two people have sex'," Wooder explains. "And it's really important not to align certain sexual practices with certain sexualities."

Teaching staff must not only be accurately informed but also feel comfortable with delivering this type of content, emphasises Streeting. Partly this means more training, but Lisa Handy, sex education forum co-ordinator at NCB says teachers who deliver sex and relationships education well tend to be strongly supported by a committed school leadership team.

"One of the basic ground rules of delivering SRE is that we're here to talk about it in a general sense, and that protects the young people and the teacher," she observes.

For schools that worry about upsetting parents, Streeting says opposition can be overstated. "I think that often you have a small number of very vocal parents who make a school hold back, so I think it's also very important for schools to engage with those parents." People who object to the inclusion of gay people in the curriculum should reflect on the long term implications of the health risks, he says.

But this is not just a public health issue: being accepting and inclusive of all young people's experiences and orientations makes a long term impact on individuals' mental and emotional wellbeing too. As Streeting points out, in the age of the internet, if young people are not getting age appropriate information at school "they'll get it elsewhere and it can be in an uncontrolled way".

Anyone genuinely concerned that LGBT pupils' sexuality is acknowledged as part of their overall education is looking at matters the wrong way round, he suggests.

"It's not about encouraging young people to go out and have sex, but allowing them to make informed choices about their sexual relationships. The most dangerous thing is young people making ill informed decisions."