The standard and content of sex education lessons vary dramatically across Scotland, according to a new report.
Although there is widespread support for Scottish Government policy, experts are worried about how this is translating into practice in schools.
Concerns have been raised about "inadequate" teaching and training, "non-existent" guidelines from local authorities, and evidence that many schools have little idea about which staff are trained in sex education.
The research, carried out for NHS Health Scotland, involved a detailed review of sex education literature and interviews with 10 representatives of national organisations with an interest in sex education, as well as staff in six secondary schools and their feeder primaries. Surveys were sent to 563 state secondary, independent secondary and special schools in Scotland, of which 392 responded.
The report, based on the work of researchers at Aberdeen and Leicester universities, describes sex education across Scotland as a "patchwork" and local authority guidelines as frequently "non-existent or poorly understood".
The 10 experts largely backed government policy but had concerns about whether it had been translated into "meaningful, consistent and sustained action at a school level".
They approved of placing sex education - now officially referred to as sex and relationship education - within the broader context of relationships and backed the shift in focus from negative aspects of sex to a more positive perspective.
While some teaching was seen as "very good", some was "inadequate". Training was perceived as "inadequate" and courses were too brief.
Although schools recognised the value of drawing on other professionals' expertise, the interviewees believed this practice was "not currently used to best effect". The most effective model was to use professionals who were regular visitors to a school and knew pupils well, said the 10 experts interviewed for the report. Instead, however, outside professionals with little knowledge of pupils were often "parachuted" in.
Some sex education experts were uncomfortable with the "dominant moral code" in Catholic schools and the implications for young people who did not adopt it, while pupils in rural schools could also have difficulties if they did not fit into "homogeneous sexual values".
The report calls for a greater range of approaches to sex education across Scotland. More research is needed into several issues, including the effect of interventions to prevent young people having sex - most research focuses on the sexually active - and the long-term impact of sex education.
The questionnaires from schools showed that more than half devised sex education with other organisations, a third did it in-house, and 10 per cent used an "off-the-shelf" programme. "Collaborative working to deliver courses is evident, but the sustained involvement of non-educational professionals is patchier," the report states.
Many schools did not know how many teachers been through training to take sex education, it adds.
There was evidence of innovative sex education, such as an interactive drama event and an AIDS awareness week planned by S3 pupils, but the main chance for pupils' involvement was through informal feedback.
Parents, meanwhile, were not usually consulted over sex education and there was little evidence of "meaningful opportunities" for them to express their opinions, as the "potentially controversial nature of (sex education) acted as a disincentive to schools to actively pursue greater parental involvement".
Jim Docherty, depute general secretary of the Scottish Secondary Teachers' Association, said a "major flaw" in the research was the presumption that people knew what constituted "effective" sex education.
He said this was highly subjective, and called for more research and detailed national guidance about what was expected of schools.
Mr Docherty felt there was too much emphasis on teachers and not enough on parents' responsibility to teach children about sex.
He also questioned whether it was really a problem relying on experts based outside schools. Children often did not open up to staff they know well, he suggested.
Sex education was no panacea, and it was "totally and completely wide of the mark" to say teenage pregnancies were purely a result of ignorance, said Mr Docherty.
Stronger links between organisations involved in sex education
Authorities to write guidelines for secondary and special schools, including sample lessons
Clear progression from primary to secondary sex education
Regular staff-training programmes
More information on the long-term impact of sex education
Assess interventions that advise young to delay having sex - most research focuses on sexually active
Look at the value of mentors for pupils involved in sex education
A range of approaches needed - not all young people can be reached by the same techniques
Pupils to be more involved in the content of sex education lessons
Greater involvement of parents and the community
School-based services to provide links to services outwith school, through a nurse or health worker - particularly important in rural areas
Disadvantaged and vulnerable young people - especially rural and excluded pupils - to have the same opportunities as their peers.