What is sex? That’s the topic under discussion for a class of Year 7s pupils at Holland Park School, west London. They are brainstorming in groups and their answers range from “making love” and “when a sperm meets an egg”, to lists of words “up and down, in and out, noise, happy, bed and slippery” and the more specific “when a man puts his dick into a lady’s vagina because they want to have babies”.

Nadia Bellott, a youth worker with specialist training in sex education, is leading the class and finding out exactly what the children know and if they understand the words they are using. When the groups share their ideas with the class, some misconceptions are cleared up. One girl asks: “Don’t you need to lose your virginity before you have sexual intercourse?” A boy also expresses his belief that women’s breasts have erections.

This is no chalk-and-talk class for the faint-hearted but the informal style is just right for the subject matter, says Nadia. “Children pick up a lot of information from television, friends and siblings, but may not really know what it means,” she says. “They are often more comfortable using their own language so I ask them to explain what they mean and also tell them the formal terms .”

She begins with a working agreement, where everyone agrees to respect each others’ views and opinions; ask no personalised questions; express no “isms” like racism, sexism or homophobia; to participate and have fun. Then she asks if anyone knows what the last item on her list TINSTAASQ means. “It means ‘there is no such thing as a stupid question’.”

In some classes, Nadia says she gives children the chance to write questions they are embarrassed to ask and place them in a box anonymously so they can be answered during the session.

She aims to get the children and leading the discussion themselves. “I want them to do all the talking. It’s important to treat them like adults, to answer their questions without being embarrassed and, if you don’t know the answer, to tell them you will find out.”

She tells the class that when people get involved in sex they have responsibilities and asks the children for their views. A lively and wide ranging discussion follows, touching on contraception, safe sex, STIs, unwanted pregnancies, masturbation, the age of consent, rape and casual sex before the children turn to feelings and relationships.

The class ends with the children writing down the qualities they want in their ideal partner and high up the list for the boys was being “buff”, or good looking