It takes two people to conceive, two to spread an infection, and two to form a loving partnership. So it would seem obvious that sex and relationships education (SRE) should be designed and delivered in a way that appeals to boys and girls equally.

But Ofsted has found that boys felt the support and advice they got in school was often aimed only at girls – and although this was not necessarily true, the perception discouraged them from seeking help. Boys report that school SRE focuses almost exclusively on negative aspects of sex, like STIs or unwanted pregnancies, or on female reproduction, the FPA says.

Research shows that boys are also less likely to go to their parents for advice, says Lisa Handy, the co-ordinator of the Sex Education Forum, meaning they get a "doubly bad deal".

"That's where you have the risk that they'll access pornography online just to work out what sex is and get answers to their questions, and be exposed to images that don't tell them what relationships and sex are really like."

A survey Brook conducted last year bears her fears out: nearly one in ten boys (9%) cited internet porn as their greatest single source of information on sex, compared to just 1% of girls. Interestingly, it also found that more boys and than girls – 15% compared to 11% – were learning most from their SRE teacher, and in this study boys were as likely as girls (9% for both) to name their parents as the best source. Girls were more likely than boys to get information from their friends, and from magazines.

But messages in media and society about what it takes to be a "real man" means boys can feel under pressure to conform to a stereotype, and that doesn't help in SRE lessons, according to Handy.

"Boys can sometimes feel uncomfortable in that mixed gender setting, and can come across to teachers as maybe being a bit jokey, acting like they know it all," she says. "This is actually one of the responses to that pressure to be super-masculine. To be sitting in an SRE lesson asking lots of questions highlights the fact you're not having sex."

And some unhelpful teaching merely reinforces gender stereotypes, rather than challenging them, or avoids discussion of homosexual relationships, according to the FPA.

How much can tailoring sex education to boys and young men specifically help? The FPA's Bout Ye project has been running in Northern Ireland since 1993, offering groups of men under 25 interactive discussion sessions exploring issues including peer pressure, relationships and fatherhood. Project officer Neil Decodts, who works in settings including the youth justice system, youth clubs and church groups, says his sessions can sometimes stretch to two hours, once participants have developed a sense of trust and dropped the bravado.

"People think young men don't want to talk, but when they get started it can be crazy," he says. "This is a chance to feel safe. We've had young men in tears ... there's real vulnerability there."

Sex educator Justin Hancock, who runs bishUK.com, a website designed for young people, says he's seen improvements in the 12 years he's been working on getting more boys and young men into sexual health services: "When I started they were much less likely to go because they saw them as being run by women, for women, about women's things." But the messaging around sexual relationships can still be offputting to young men, he says.

"Often their role is seen as being a kind of predatory man who always wants to have sex and doesn't take responsibility – it's all about protecting women from marauding sexual beasts. A lot of assumptions made around young men just aren't true. They're given really short shrift, by practitioners as well – a lot of them are wary of working with young men, they find them loud and shouty, and say they're not really interested. They are really interested, but we need to get the message right."

One way of doing that, Hancock says, is by taking a sex positive approach to teaching – talking openly about pleasure and how good sex can be. "If you just talk to young people about STIs and how they're damaging that's very sex negative, and lots of people, particularly young men, are going to switch off, because they'll think 'I've been told sex is great'." To teach young men about about STIs, Hancock gets them to list different sexual activities and rate their safety.

Understanding what young men want from sexual health services – by asking them – is also key to drawing them in to an environment where you can then provide education, he adds. "We put young men at the heart of it, and say we've got these amazing condoms, different shapes and sizes, condoms that increase pleasure for your partner ... something as simple as saying we know the condoms you want gets them through the door."

Mixed gender groups are also important if boys and girls are to learn about each other, of course. But are there particular topics that are best discussed in single sex groups? Ed Hart, boys and young men's worker at Brook Cornwall, says porn is one example.

"Pornography is influencing so much of what we're working with them on. With a lot of young women you're saying it's not wrong to think the stuff in porn is vile and disgusting, but to boys [you're saying] it's all right if you're drawn to it, but try and remember it's a fantasy world, it's not a 'how to' for good relationships."

Young men appreciate the opportunity to talk about porn without the kind of instant telling off they'd get at school, Hart says, and that's where the chance comes to dispel misconceptions it may be giving them about sex and relationships.

"[At school] there isn't the space for them to explore it in an environment where they might be guided. They get told off for it and then it goes underground."

Focusing on girls alone mistakenly suggests boys are powerless to take responsibility for their behaviour and actions, says Handy. "You're putting all the responsibility on the girls and that's not how relationships work – healthy relationships are about respect for each other and being able to negotiate what it is you want and need," she says.

"If you just give it to the girls you're only dealing with 50% of the population – you're only doing half the job."

• This article was amended on 2 August 2012. In the original, Neil Decodts was misnamed as Neil Roberts.