But the dilemmas it creates for teachers - and ministers like England’s Education Secretary Ruth Kelly - will increase, given the moves to combine education and welfare services, and the tendency of politicians to want to be in control.

Strictly speaking, Ms Kelly can say school governing bodies, not ministers, decide what children should be taught about sex and that parents can withdraw their children from those lessons. But then heads and governors - and not Ms Kelly - are also supposed to have operational responsibility for school discipline. Yet she has felt the need to sound off about low-level classroom disruption all week - in response to Conservative noises about school behaviour.

It is extremely unlikely that any New Labour minister, whatever their religious persuasion, would be able to resist similar challenges over school sex policies. Especially since schools are expected to do more now than simply teach about sex. They are also becoming sources of clinical advice and treatment for pupils seeking contraception or abortion. This may be the job of on-site medical staff, rather than teachers, but schools are implicated in the controversial questions that then arise - particularly those over the medical confidentiality afforded to minors which, if nothing else, conflict with schools’ need to work with parents as partners.

The understandable unease this produces is reflected in the belief of most teachers that an under-age girl’s parents should be told if she seeks an abortion. Supportive parents are clearly the ideal. But situations in which not telling the parents can seem the lesser of two evils are not difficult to imagine.

But the law is based not so much on practical arguments as on the primacy of the child’s right to confidentiality over the parents’ right to know.

And the law is the responsibility of ministers, not teachers.