So who exactly needs the sex lessons?
teachers delivering sex education lessons are often woefully ill-informed, a Birmingham University study has found. Many identified sexually transmitted diseases incorrectly and misunderstood what Aids is.
Academics interviewed 155 sex education teachers from 19 secondaries. Only one was a full-time personal, health and social education teacher. The others taught subjects such as science, English and physical education.
The interviews revealed significant gaps in their knowledge. Almost half felt that they did not know enough about contraception to teach pupils to adequately protect themselves. Fewer than half knew the emergency pill could be used up to 72 hours after unprotected sex. And only 28 per cent knew that the emergency pill is 85 per cent effective.
Fewer than a third correctly answered questions about Aids, and many were confused about the difference between the disease and the virus which causes it.
One in 10 teachers was unable to correctly identify chlamydia, the most common sexually transmitted infection. Fewer than half realised hepatitis B could be sexually transmitted. Some teachers identified non-existent sexually transmitted diseases, such as hepatitis H and coxiella.
Three-quarters said they had received no up-to-date information about sexually transmitted diseases.
Of particular concern were the 60 per cent of teachers aged 40-plus. The report said: "This age group was exposed to the mass HIVAids campaign of the 1980s. Information and education received then would be outdated now."
The report also said: "Out-of-date teaching is going to have implications not only for pupils' sexual health knowledge, but also for the implementation of local and national sexual health initiatives."
The majority of the teachers admitted feeling ill-prepared for sex education classes. Only one in 10 said they had sufficient resources to teach the subject.
British teenagers have the highest rate of conceptions in western Europe.
But resources to teach about teenage pregnancy, parenthood, termination and abstinence were particularly scarce.
And a third of teachers actively disliked teaching sex education, suggesting they were unlikely to bring enthusiasm to their classes.
The report said: "A greater emphasis must be placed on continuous professional development and updating both teaching skills and knowledge base. Those that have no interest or lack the confidence to contribute to the lessons only ensure that pupils continue to have inadequate sexual health knowledge."
* 'Knowledge and attitudes of secondary school teachers regarding sexual health education in England', by Jo Westwood and Barbara Mull in 'Sex Education', vol 7, May 2007