Researchers Katie Buston and Daniel Wright from the Medical Research Council in Glasgow have found that the 11 hours of sex education a year young teenage girls normally receive in the average secondary is much less likely to influence their attitudes and behaviour than the informal network which operates daily.

However, most appreciate the information they receive at school.

The study involved a sample of 39 girls from six east of Scotland secondaries and concludes that that sex education should not be “dismissed or underestimated”, although it could be improved by perhaps lowering the key age it is aimed at. Most lessons take place in S3 and S4 but many girls are having sex at an earlier age.

Fewer than a third of those surveyed cited sex education as one of their main sources of information and it rarely met all their needs. “The salience of one’s close friends’ experiences seemed far greater than that of school sex education,” the team comments in the latest edition of the journal Sex Education, published this month.

Policy-makers also expect too much from sex education in cutting teenage pregnancies and sexually transmitted infections. “As such, more thought needs to be given to the place of school sex education in community-wide approaches to promote the sexual health of young people,” the researchers state.

They add: “Partnerships between schools and other agencies - in the statutory and voluntary sectors - are needed, providing multiple access points for young people to the information, advice and skills they need . . .

“Relying on the school alone to promote young people’s sexual health has limitations, but ignoring the school may mean missing out on a potentially powerful site for shaping the behaviour of at least some young people.”

Some aspects of health education programmes were valued by young people. The researchers say: “Specifically, the young women valued: being shown different kinds of contraceptives, being told how effective each is, how to obtain them and plan to use them with one’s partner, and or how to use them (in some cases having a chance to practise putting a condom on a model phallus); being taught about STDs (sexually transmitted diseases), including HIV and Aids, how they can be contracted and prevented and or where to go to get tested; and being taught how to say no.”

Some girls said they learnt nothing new, that the information was too late and that parts of it were unrealistic. One girl who was 12 when she had the first of several sexual relationships, said: “I think because I had sex before really you got much sex education, it didn’t really change what I was thinking already, but maybe if I had sex education first it might have made me think differently about things.”

Another said: “I think we could have done with it at that age (primary school). A lot of people when they go up to first year they go, ‘we’re older now, we’ve got to lose our virginity’, and a lot of people have done that.”

The researchers acknowledge that only a minority of pupils have sex in their early teens but they are extremely important in public health terms.