Joan Smith: Let's talk about sex – to children

Some people have sex on the brain. I'm not offering this as a profound insight into human nature – I don't do those on Thursdays – but it's such an obvious statement of fact that I'm always surprised when someone fails to appreciate it.

Imagine a group of evangelical Christians, for example, who are so obsessed with homosexuality that they tried to bring a case under the unlamented Section 28. They've also opposed the right of gay couples to adopt, funded an evangelical registrar who didn't want to process civil partnerships and paid for the defence of a couple who refused to allow a gay couple to stay in their guest house.

Now, if the very same people were to tell you that primary schoolchildren as young as five were about to be exposed to "shocking material'"of a sexual nature, how would you react?

You might infer that these furious "family campaigners" have an agenda, possibly linked to a literal interpretation of Scripture that doesn't have anything much to say about modern life. You might even applaud what appears to be an attempt to provide schoolchildren with unsensational information about sex in a form they can easily understand. If so, it's a fair bet you don't have connections with our old friends at the Christian Institute, who've come up with a "disturbing dossier" attacking several books which have been cleared for use in schools, including one called How Did I Begin? by Mick Manning and Brita Granstrom.

Among the images in the book is a drawing of a couple in bed, accompanied by an explanation of how the man's sperm enter the woman's body. (OMG, you mean I wasn't found under a gooseberry bush?)

I can imagine the image prompting giggles in the classroom but that's largely because the cartoon couple is hidden by a hideous duvet cover; it's a lot less explicit and certainly less erotic than images I've seen on MTV, fashion shoots and CD covers. We live in a culture where sex is used to sell any number of things, from perfume to cars to clothes, and these fantasy versions of sex don't warn about the danger of infections, abuse and under-age pregnancy. So I'm delighted that sex education has been a compulsory component of the science education area of the national curriculum since 2008, while older children are taught about safer sex, contraception and how to resist being pressured into unwanted sex.

The evidence is that it's working. After decades in which the UK had one of the highest teenage pregnancy rates, the under-18 conception rate fell in 2009 to its lowest since the early 1980s. But there are still 38.3 conceptions per thousand girls aged 15 to 17 and most of these pregnancies are unwanted: almost half the girls under 18 went on to have a legal abortion, while three-fifths of the girls under 16 did the same.

We also know that it's a class issue, with girls from a manual social background eight times more likely to have a teenage pregnancy than their peers from managerial and professional families; one of the UK's most deprived areas, the north-east, has an under-age conception rate almost twice that in the east of England.

The last Labour government missed its target of halving the teenage pregnancy rate within a decade, but ministers had the guts to insist that sex education should be included in the national curriculum. I don't expect to find favour with a bunch of homophobes and anti-abortion zealots who believe, among other things, that the Bible is "inerrant". But I cling to the hope that it isn't just me who recognises that evangelical Christians have weird, punitive attitudes to sex and shouldn't be allowed any influence over sex education. Far from sexualising five-year-olds, these lessons provide the skills they are going to need to enjoy sex as young adults, without being damaged by ignorance, outside pressure or abuse.