Sex education classes do not reduce the number of teenagers who practise unsafe sex, according to research that suggests parents can play a more influential role.
A study published in the British Medical Journal indicated that teenagers who received a special programme of tutoring were no more likely to delay having intercourse than pupils who received conventional guidance.
One third of teenagers in both groups had sexual intercourse by the age of 16 and equal numbers reported using condoms, according to the study by the Medical Research Council's Social and Public Health Sciences Unit at Glasgow University.
Teenagers knew more about sexual health and enjoyed marginally better relationships after the improved programme. But the authors said: "It did not reduce sexual risk-taking in adolescents."
One important factor was the degree to which parents kept an eye on their youngsters. Those who were closely monitored in the evenings and weekends were much less likely to have had sex at 16, according to the study of 5,854 teenagers from 25 secondary schools in east Scotland.
Dr Daniel Wight, who led the study, said the findings implied that sexual education classes had a limited impact on teenagers' behaviour and other methods were needed to help young people to make responsible decisions.
"It could be that the current level of sexual education has gone as far as it can do in influencing sexual behaviour and we need to complement it with different approaches."
Dr Wight suggested weekly drop-in clinics at schools, which teenagers could attend when they were ready to embark on sexual relationships, rather than formal lessons for a class of pupils who were all at different stages of sexual development.
He added: "Parents seem to be important. There seems to be clearly scope for parents to be given more help in helping their kids to avoid unwanted sexual risk-taking."
A second report in the BMJ says that schemes designed to prevent teenage pregnancies do not delay sexual intercourse, improve the use of birth control or reduce the number of conceptions.
Britain is second behind the United States in having the highest teenage pregnancy rate in the industrialised world – a record that has been blamed on the failure to prepare young people for today's looser sexual attitudes.
Researchers in Canada reviewed 26 projects in North America, Australia, New Zealand and Europe intended to reduce unwanted pregnancies in the 11 to 18 age group. They suggest that projects should be aimed at children much earlier, perhaps as young as five, and learn from countries such as the Netherlands, which have low pregnancy rates.
"This review shows that we do not yet have a clear solution to the problem of high pregnancy rates among adolescents in countries such as the US, the UK and Canada," the study concludes.