It was the high-pitched screams and plaintive cries of "Get it off me! Get it off me!" that alerted me that all was not well outside my classroom one wet lunch break. Charlie, all 5ft 8in of him, cowered against the wall as a group of Year 7 girls waggled worms in his face.
Seeing his tears, I realised I had arrived just in time. The mood was turning into Lord of the Flies, except the perpetrators were wearing ballet flats and headbands. I explained to them that this behaviour was cruel, both to the unfortunate worms and to Charlie, and went back in.
It was only then that the gender reverse struck me. When I was a girl, it was the boys who chased us with worms.
The girls have only been with us since September, when we went fully co- educational. And there have been other surprises: Gemma, in class, clutching a pink hot water bottle to her stomach and groaning softly, for instance. Initially I feared an oestrogen spillage, until she explained that she had just pulled a muscle in her fencing lesson. Fencing? I was expecting skipping.
Olivia and Ellie provided yet more surprises with their battle plan to overthrow Grendel and help Beowulf to victory. While the boys' strategies were full of blood, guts and testosterone, theirs had three female Amazonian warriors skilled with bow and arrow: defeat by stealth and intelligence, not bare brawn. Impressive.
When we went co-ed, part of me was expecting the school would suddenly awash with glitter and pink. I was wrong. There has been no outbreak of My Little Pony or Miss Kitty. No flowers or hearts dotted over their "i"s. Just a hint of defiance as they roll over their waistbands to shorten their skirts.
The boys have responded well. Around their toilet is a fog of Lynx, that never used to be there, as the lads up the ante in personal grooming skills. Now they just need to grasp the part about washing first.
Nurse has been on stand-by with the nail varnish remover, but so far it's just been Henry and Ben who needed those after a weekend party. None of the girls has needed the make-up wipes either, although perhaps now someone will speak to Alex about the foundation he uses that seems to be turning his skin orange.
The media seems to panic about boys - tales of woe about their underachievement, their failure to perform, be they black, white, working class - but never girls. Initiatives are introduced, money spent, government funds pledged and action taken. Why, I wonder, has no parallel action ever been taken for girls? I guess they don't need it.
Wrong again. In 1996-97, women overtook men as a proportion of the undergraduate population, which isn't bad going if you pause to consider that some universities only first offered women full degrees in 1948. Girls have come a long way very quickly. Yet 10 years later, the Equal Opportunities Commission found that the full-time pay gap between the genders was 17.2 per cent. Rather a dull, meaningless figure, until you realise that, over the working life of an average woman, this equates to her having lost out on pound;330,000. I wonder what our girls are going to make of that. Worm wiggling? That will just be the start.
Julie Greenhough, Teacher of English at a London independent school.