The research was conducted by academics at the University of York and Liverpool School of Tropical Medicine.
Amanda Mason-Jones, study lead author, called for a radical rethink. ‘Most people agree that sex education should start early and focus on relationships, not just on the mechanics of sex,’ she added.
‘Most also agree it should be inclusive and sensitive to a range of sexualities, including not assuming that all young people have started to have sex.
‘Equally, few would disagree that we need to reform current approaches to take into account new risks from digital communications and social media, and that schools are a good place to encourage the development of healthy relationships.’
The findings come from the first review of its kind to look at ‘measurable biological outcomes’ among teenagers.
Dr Mason-Jones, who looked at lessons in Africa and Latin America, as well as the UK, said it is not always clear what was being taught in classrooms. But the review of eight studies and more than 55,000 children worldwide showed little or no effect on the number of children infected with syphilis and herpes, or on teenage pregnancies.
Interestingly, keeping children in school for longer, and not allowing them to drop out, cut disease and reduced pregnancies by about 22 cases per 1,000 girls.
Dr Mason-Jones said: ‘In the UK the only mandatory part of sex education is the biology part, the mechanics.
‘It assumes only heterosexual sex for a start. It could be introduced much earlier if we talked about love and relationships. Young people would be much more open to this and parents much less concerned perhaps.’
Education Secretary Justine Greening has told MPs she was prepared to re-examine compulsory sex education to ensure children made informed choices.
Pressure groups have repeatedly called for PSHE – personal, social, health and economic education– to become statutory. But a separate review of studies carried out mainly in the UK found sex and relationship education was often ‘out of touch with many young people’s lives’.
Writing in the journal BMJ Open, researchers said young people dislike being given it by their teachers, raising the prospect of specialists being used.
Norman Wells of the Family Education Trust said the York and Liverpool study ‘exploded the exaggerated claims frequently made about the effectiveness of sex education programmes’. He added: ‘The evidence to date has been limited but this international study examines measurable biological outcomes such as pregnancy.’