Children, notoriously, do not always learn what teachers think they are teaching. Nowhere is this clearer than in the area of personal relationships in which the human species seems doomed forever to discover old truths anew. Take sex - or biology as they call it at some schools.

Ben is a keen science student who always gets As. The teacher, he says, is “full of interesting facts” and “really good at discussing things”. Like I “Mum,” he asked one day when lazing in the bath. “Mum, is it true that when you adults have sex the man puts his hand up inside the woman’s vagina?” Ben is 12. Sex holds for him the kind of horrid fascination that spiders have for flies. His mother pondered his question. It seemed to put foreplay on a level with veterinary inspection of pregnant cows. “Sort of,” she replied.

He shuddered. “Well, I think it’s disgusting,” he announced, shaking water out of his hair.

In this case the adult felt a desire to set the record straight. And, of course, everyone wants yong people to grow up thinking sex is natural. So mother rallied. “It’s not disgusting. How could a couple have sex if they didn’t touch each other? How would they know they were ready?” Ben looked at his mother pityingly. “They could ask! Anyhow, touching is one thing, but putting your hand inside - ugh!” These situations are always tricky. As an adult, one doesn’t want to fall into the: “Well I know better than you because I’ve done it and you haven’t” kind of 12-year-old childishness. But, on the other hand, there is a point in sex education in which more theoretical detail does not become necessarily more instructive. Ben’s mother compromised on: “It won’t seem so disgusting when you’re older.”

Ben went on brooding over the undignified nature of copulation. “And I know other things you adults do. You rock back and forwards - that’s to help the sperm go further up inside - and you moan, to encourage the man. See, Mum, I know.” And he disappeared under the water.

Ben’s mother got a bit anxious. What were they doing at school? Telling him too much before his time? Should she complain?

Ben emerged, shaking his head. His mother asked: “How do you know all this? Is it at school? Don’t you think they ought to tell parents that they’re going to talk about this kind of thing?” “Oh Mum, you’re not going to make a fuss, are you?” He sprang out of the water and grabbed a towel. Puberty had not yet laid its hairy hands on his satiny body. He looked in the mirror, grinning.

“In science, of course. In science. He’s a brilliant teacher.”

“I don’t know,” she said, “if that is science. What about feelings and relationships? What about falling in love?” Ben widened his eyes. “But Mum, we’re talking about the mating behaviour of our species. Of course it’s science!”