Under the “be healthy” aim of Every Child Matters, schools are instructed to ensure that children are sexually healthy. And a TES survey of more than 2,000 teachers found that half believe that sex education should be compulsory from primary school. Almost two in 10 would like to see this starting from Year 3.

Ralph Jaggar, head of Ackton Pastures, agrees. “You need to cover sex education before children reach puberty,” he said. “Some girls start their periods at age 8.

“Children need to be prepared so that, when changes happen to their body, it doesn’t come as a shock. They don’t wonder why they’re suddenly feeling irritable. They understand it’s all part of growing up.”

At the school, the nurse introduces the topic in the summer term of Year 3. She begins by discussing emotions: what makes pupils happy or sad?

This leads on to a discussion of bodies and how hormonal changes can influence moods. The nurse holds up an outline of male and female bodies, and asks pupils how they know the difference between boys and girls. She then brings out a succession of body outlines, illustrating the changes from pre-pubescence through to adulthood.

“She asks, ‘What do you call private parts of the body?’” said Mr Jaggar. “They’re encouraged to shout them out. Then she says, ‘The actual name is a penis’. The kids have a little giggle and then they’re fine.”

Follow-up sessions are taught every year, until pupils are ready to discuss contraception and sexually transmitted infections in Year 6.

“Preventing teenage pregnancy is about giving the right sort of information,” Mr Jaggar said. “If we don’t give children information and guide them, then teenage pregnancy is our responsibility. But if we give them the right information early enough, then teenage pregnancy becomes their responsibility.

“You can’t be responsible if you don’t have the information to make choices.”

The latest figures available, for 2005, show there were 39,804 conceptions by under-18s in England, or 41.3 pregnancies per 1,000 teenagers. Although the rate had steadily dropped over the previous 10 years, it was still the highest in western Europe: three times that in France, and six times higher than the Netherlands.

Before introducing the scheme, which originated in the Netherlands, Ackton Pastures held meetings for parents. But surprisingly few attended. Even fewer withdrew their children from the lessons.

Mr Jaggar has since found himself drawn into unexpected conversations with 8-year-olds. “I was sitting at lunch with a table of girls and they were talking about periods,” he said. “They weren’t embarrassed to talk to me about it.

“It was one of those golden moments you get in schools.

“It’s about ridding this taboo about sex. We’re doing it slowly but surely.”

Jonathan, 8, agrees with smashing taboos. “I like learning about what’s inside your body, so you know how you work,” he said.

“Sometimes, when they said words like ‘penis’, everyone giggled. But it’s not just a giggle: it’s a part of the body. I don’t know why people get embarrassed.”