Sex education alone is not enough to cut pregnancies and abortions among teenagers in the UK, say experts.
The study involved 14-year-old school children
A Medical Research Council study, in the British Medical Journal, examined sex education in 25 secondary schools.
It found pregnancy and abortion rates among girls taught with an enhanced sex education scheme were the same as among girls given conventional sex education.
The authors say other sexual health strategies are urgently needed to cut the UK's teenage pregnancy rate.
The rate in the UK is the highest in Western Europe.
All schools in England and Wales have to teach sex education to 11-14-year-olds as part of the science curriculum.
In Scotland, schools are not obliged to provide sex and relationship education, so provision is patchy.
England has also had a strategy for reducing teenage pregnancy rates running since 1999, with a target of halving the under-18 conception rate in England by 2010.
Pregnancy rates among under-18s are currently at their lowest for 20 years in England.
Part of the strategy is improving the provision of sex and relationship education, which has sparked mixed views.
Some believe education will help and recommend children as young as 10 should be taught about contraception.
But others say it fuels the problem, encouraging children to be promiscuous.
Investigators from the Medical Research Council evaluated the impact of an enhanced sex education programme, known as SHARE.
The main difference from conventional sex education is SHARE's intensive teacher training and focus on developing skills using role-playing, rather than simply providing information and discussing values.
For example, teachers are trained how to teach children skills so they can negotiate sexual encounters, handle condoms and access services.
The study, which focused on 25 Scottish secondary schools, found SHARE did have a positive impact on sexual health knowledge and quality of relationships, and was preferred to conventional sex education by both pupils and teachers.
But it had no impact on the number of pregnancies or abortions among school girls.
Lead researcher Dr Marion Henderson said: "It is clear that economic circumstances still largely determine the likelihood of teenage pregnancy.
"To have a stronger impact, alternative interventions should be considered."
She suggested parents should be more involved in providing guidance to their children.
Director of the fpa (Family Planning Association) in Scotland, Tim Street, said: "SHARE and other sex education programmes like it are good. But they are just one tiny piece of the jigsaw.
"There are very few areas in the UK that are doing the whole gambit of information, services and education.
"Adults are not setting the best examples for children. There is also a severe lack of funding for sexual health."
A Department for Education and Skills spokesman said: "Sex education is only part of the story.
"High quality Personal Social Health Education is a vital part of a successful strategy which must also include easy access to advice and contraception for young people.
"Our research shows that areas which deliver their strategies in this way have seen much greater successes in bringing down rates and our latest guidance urges all local authorities and primary care trusts to work in this way."