Those who can, do, according to the old saying, and those who can’t, teach. That has always seemed to me unfair. However, I have come to think that those who can’t teach, teach sex education.

Judged by its results – not a bad way of judging – sex education has been an utter failure. The increase in sex education here in recent years has coincided with an explosion of unwanted pregnancies and sexually transmitted disease (STD) far worse than anywhere else in Europe. Since the government’s teenage pregnancy strategy was introduced in 1999, the number of girls having abortions has soared. You might well be tempted to argue that sex education causes sexual delinquency.

Only two months ago the Health Protection Agency reported that a culture of promiscuity among the young had driven the rate of STDs to a record. Almost 400,000 people – half of them under 25 – were newly diagnosed, 6% more than in 2006.

When something fails, the usual procedure is to drop it and try something else. With sex education, the worse it gets, the more people cry out for more of it and earlier. Ministers are considering whether to make schools offer more sex education, offer it earlier and deny parents the right to withdraw their children from it.

Last week the Family Planning Association – now calling itself the fpa, having joined other charities in a mad rush to reduce themselves to a couple of lower-case letters – published a comic-style sex education booklet for six-year-olds to be marketed in primary schools for use in sex and relationships lessons. It has printed 50,000 copies of Let’s Grow with Nisha and Joe, and tried it out in more than 50 primary schools; it hopes to encourage schools that have shied away from sex lessons to take them on with Nisha and Joe. Oh dear.

There’s nothing wrong with the pamphlet itself. Admittedly it’s more of a dreary workbook than a “fun” comic, but there’s nothing that would startle a child or should upset even the most conservative of “family campaigners”. The rudest thing is a drawing of two children, naked, with instructions to draw lines connecting interesting bits of their bodies with the appropriate words. This is all to promote discussion of sex and relationships when children are young enough not to feel self-conscious.

It seems to me highly unrealistic (given that 25% of children leave primary school struggling to read and write) to assume that many six-year-olds could begin to read the labels “testicles” or “vagina”. And it is infuriating, given that medical-style euphemism has triumphed over plain English, that the authors have chosen one that’s wrong. “Vagina” does not mean the external genital organs, commonly referred to as “front bottom”. It comes from the Latin for sheath or scabbard and means what that suggests. The correct word would be “vulva”, but the ill-educated educationists blithely impose inaccuracy on our tiny children. However, that is not what I most object to.

What I object to about the book is what I object to about sex education as a whole (quite apart from its failures). Sex education – particularly compulsory and standardised sex education – is based on mistaken assumptions. The first is the pervasive assumption of equality – that is, that all six-year-olds or all 11-year-olds or 15-year-olds can discuss the complexities of sex in the same form in the same way. That’s nonsense. Children vary in intelligence and progress. Some young children can easily decipher words such as “urethra”; others may never be able to read them.

More importantly, children and teenagers mature at different ages and come from different backgrounds with different family expectations. You cannot talk the same way to a shy 13-year-old who hasn’t had her first period to another who is well acquainted with the darker recesses of the school bike shed. Some boys are men at 11 and 12, physically; others are children until much later. Some children’s parents find it acceptable that their sons and daughters are having sex at 13, while others would be shocked: you cannot talk to all these children together. It would puzzle and offend them and might do them serious damage. And it undermines the authority of those parents who do not share the values of the teacher, or of the majority of the other pupils. It is wrong to assume that people want equality in such matters. They want differences.

Children and families and moral values are not equal, neither within schools nor outside them. They simply aren’t the same.A sensitive teacher will try to make allowances, but there is a shortage in this country of good and sensitive teachers – hence the crisis in education.

Another mistaken assumption is that sex education ought, necessarily, to be entrusted to teachers, given how wildly they vary in ability and in moral attitudes. The thought that the government is considering making sex and relationship education compulsory in schools is terrifying. I can hardly imagine anything worse than subjecting a sensitive child to guidance on such matters from an inexperienced and politically correct teacher, who is neither well informed nor self-critical.

The relationships between sex, love, babies, crime and disease are too explosive to be left primarily to such a person, or to any person apart from the parents. Of course where parents can’t, or won’t, guide their children on such matters, the duty falls on teachers. Some may do a good job, although the evidence isn’t encouraging. But none should take it on without parental consent.

It always amazes me when people complain that people don’t talk about sex and there’s not enough information about it. The truth is, you can hardly avoid it. Newspapers, magazines, chat shows, blogs, internet information sites, doctors’ surgeries and all the rest are groaning under the weight of information about sex, contraception and relationships. Some of it I think is good; some of it you might think is better. And that’s the point. Schools shouldn’t be required to impose sex education, still less a standard sex curriculum on us. We should be able to pick and choose for our children among the infinity of information out there.

Channel 4’s The Sex Education Show, for instance, strikes me as informative and helpful but depressingly vulgar. Others might find it tastefully frank. It’s up to us to choose. Teacher, leave that child alone.

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