How do you make sure everyone is doing it?
Sex educators take heart from Labour's election victory. They want sex education to become a key part of the national curriculum by the year 2000. Gill Lenderyou of the Sex Education Forum says: "The time has come to overhaul the curriculum and have personal and social education as its central core. "
The Forum - which represents 38 children's organisations - is calling for better initial and in-service training of teachers in PSE, a PSE co-ordinator in every school and a curriculum which puts the "fourth R" - relationships - first in school culture and classrooms. But can they take the Government with them?
One significant change is the publicly-expressed intention of the departments of health and education to work together. (Under the last government, many specialists blamed the "woolly" lead from education secretary John Patten, a Catholic traditionalist, for the failure to make progress on halving conception rates among under-16s.) "We see the working together of health and education on these matters as being absolutely essential," Tessa Jowell, minister for public health, says. Schools are seen as an important avenue for delivering the new public health goals, among them reducing teenage pregnancies.
The Government is poised to set up a task group on personal, social and health education, to look at how health and education can work together to promote "healthy schools".
Sex education is currently fragmented between statutory and non-statutory aspects of the curriculum, weakened by parents' right to withdraw their children and, often, teachers' lack of confidence.
Some schools, with religious sensitivities among parents and plenty else to worry about, are "simply not doing it", said Dr David Winkley, until recently a headteacher in Handsworth, Birmingham and now a member of the Government's task force on standards.
Campaigners are disappointed that the White Paper on education, Excellence in Schools, makes little reference to PSE, while the White Paper expresses the Government's intention to introduce citizenship and parenting education.
Sex education provokes such strong passions that no changes to legislation or departmental advice will go unscrutinised, and it is impossible to please everyone.
However, there is a consensus that the moral climate of 90s Britain has changed. There is more understanding of the situation of one-parent families, less rigidity on the form the family should take, a free vote is to be held on the age of consent for homosexuals, and even the Conservatives have adapted to the changed social landscape.
Sex education is seen as inadequate by young people themselves. Of more than 1,000 young people interviewed by the Sex Education Forum at the BBC's Big Bash last year, less than half the girls felt they had enough information on HIV, abortion, gay relationships or sexually-transmitted diseases.
The British Medical Association has called for "high quality sex education as an essential part of schooling which supports young people's development and prepares them for adult life".
Among teachers there is some support for a PSE revolution. The National Association of Head Teachers has proposed a model curriculum which has values, PSE and health education at its heart. Work on values by the School Curriculum and Assessment Authority has also focused on non-academic aspects.
Campaigners believe they have education minister Estelle Morris on their side. One said: "She likes schools, young people and teachers. And she understands PSE."
People advising Tessa Jowell believe she is switched on to the type of services young people need to accompany the sex education. "She realises the need for early sex education, and that you have to talk in a different way to young people," says Alison Hadley, of Brook Advisory Centres, which run services for young people. Tessa Jowell is understood to acknowldege the need for some under-16s to have confidential contraceptive advice.
But observers question whether the radical women of New Labour can take the more socially-conservative men with them. Can David Blunkett, who voted against reducing the age of consent for homosexual men, be persuaded to put relationships - including same-sex ones - at the heart of the curriculum? Could Christian Tony Blair stomach the advertising of contraceptive clinics in secondary schools, particularly if they also referred some young people for abortions?
Yet traditionalists and liberals express faith in David Blunkett. Gay rights campaigners believe that the Secretary of State may vote differently in the forthcoming free vote. "He's a very moral person," said one. "He doesn't like prejudice and discrimination." The sex education lobby believe he is "changing and developing".
Yet right-wing pundits opposed to sex education also put their faith in him. The Muslim lobby, who recently visited the DFEE, profess themselves content with the status quo - and see no signs of imminent change.
Diane Abbott MP, whose Hackney North constituency contains many young single mothers, believes there is a schism in the Government's attitude, but says it springs from financial considerations. "There are two strands to Government thinking on young people," she says. "One is a holistic, realistic view, the other is Treasury-driven. On single parents, it's women pushing the holistic view because they know 'there but for the grace of God go I'. And they know how hard it is. But I suspect the men will prevail. Both the last government and this one seem obsessed by the Holy Grail of cutting the social security bill."
There are concerns among the sex education lobby that the broader educational picture could be lost in favour of the relatively cheap and simple option of targeted interventions. Social security minister Frank Field mooted in August that girls "at risk" of becoming teenage mothers should be identified from their poor educational achievement.
"Sex education can not be expected to pick up the tab for social problems, " said Gill Lenderyou. "It's part of a whole package, and if we think it's going to sort out teenage pregnancy single-handedly - it's just not possible. "
Sex education alone will not reduce teenage pregnancy. And looking through the other end of the telescope, teenage pregnancy is now but one small part of what modern sex education - better understood as personal and social (and probably health) education - hopes to address.
"If you believe that developing self-esteem is important in achievement, and how you relate to others is a very significant aspect of your future life, school organisation has to be arranged to maximise that," said Anne Weyman, chief executive of the Family Planning Association. "Schools should be contributing to an understanding of what it is to be a human being."