The local authority is demanding action. According to Oriel Greer, the LEA adviser who seems to be on permanent secondment to St Brian's these days, our pupils are placing an intolerable burden on the local sexual health services. The borough has shot to the top of the teenage pregnancy and sexual infection league tables, and we're to blame.
So today is sexual awareness day. Not surprisingly, this morning's cover list spans the width of the staffroom wall - few people can stomach the idea of an intimate discussion about chlamydia with 10C. But there is a hardy band of enthusiasts. Sandie McSniff, head of PSHE and weirdness, has volunteered to organise the day, assisted by Anna Hatch, our alarmingly fecund English teacher, and Ramona Lynch, one of the Year 12 teenage mums.
Anna arrives unusually early - "no school run today!" - with her twins Hermione and Jocasta in tow as today's learning tools. The people carrier pulls up complete with roof rack piled high with changing mats, breast pumps and incontinence knickers. The strategy seems to be to terrify the kids into a life of chastity. Ramona wheels in six-month-old Darren Junior, who is sucking on a Mr Burger Happy Meal.
The boys' workshops are being led by John Baller and Orlando Jones. John is a veteran of such events, his speciality being a graphic account of his experiences as a soldier in Aden - "where men were men, and the camels were nervous". He is hopelessly out of his depth here, and after a few minutes is sitting transfixed as a bunch of 15-year-olds debate the relative merits of penetrative sex and mutual masturbation. John's shambolic session ends with him attempting to demonstrate the pain of childbirth using a rather tatty rugby ball. "Imagine spending 14 hours trying to squeeze that out of your jacksy!" he yells, to the boys' bemusement.
Orlando, as an absentee father of five children spanning several continents, is more successful, and his tales of impoverishment at the hands of the Child Support Agency bring a nervous hush to the room.
The girls aren't faring well. Anna has brought in her birth videos. The first, from the early 90s, is of poor quality, just some blurred images of Anna huffing and pushing to a soundtrack of Clannad songs. However, her metamorphosis into earth mother is accompanied by a dramatic improvement in video technology. The quality of "Birth of Electra, Cornish rock pool" is first-rate. But the no-holds-barred story of the twins' arrival is too much for some; three Year 10 girls burst into tears and start pummelling the battery babies that have been left in their care. Cashell's is later found in the toilets stuffed into a sanitary towel bin. Cashell says she found it impossible to send text messages while carrying a baby.
The day concludes with a talk from Ramona on the reality of life as a teenage single mum. This consists of her giving a list of clothes shops that aren't security alarmed and useful tips such as the fact that six-month-old babies can't be prosecuted for shoplifting. Well, it's a kind of education.
Next week: Is Blaine a closet heterosexual?Charity Begins: Adventures of an NQT, Charity Casement's diary of her first year at St Brian's, is available from TES Books, pound;2.99. Tel: 0870 444 8633 or visit the TESBookshop at www.tes.co.uk