There is sniggering going on at the back of my classroom. I’m used to this because after five years in teaching I’ve developed a skin thicker than a rhinoceros hide, and the slings and arrows of teenagers don’t bother me any more. I’ve come to accept that being a figure of derision is an unwritten part of the job, and poking fun at your teacher’s dress senseshoesmake-up is a rite of passage for pupils that can’t be ignored. If I was Claudia Schiffer, teaching in a Chanel suit, I’m certain I would manage to attract censure, at least from the female element of the class. The most damaging thing that can happen to any adolescent follower of fashion is to turn up at school wearing the same item of clothing as your teacher, and let me warn you: girls, I’m not too old and decrepit to have the odd look round Top Shop now and again.

Gemma text = But anyway, the sniggering. I’m more aware of it than usual because for the past 20 weeks I’ve been struggling to cover up the increasingly uncoverable - my pregnancy. No longer can I blame a surfeit of Jaffa cakes. It is obvious to my hypercritical teenage audience that my husband and I have done the dirty deed at least once, and I am now displaying the results. You can see them battling with a potent mixture of distaste, incredulity (yes, I managed to pull) and interest. Wanting to enjoy a rare moment of power for as long as possible, I ignore the sniggers and carry on with the register, aware that some UN-style diplomacy is rapidly reaching its conclusion. “You ask her!” “No, you ask her. I’ve already got detention on Friday.” They finally nominate a reluctant volunteer, who sidles up to the desk trying to rearrange her features into one of concern. “Miss? Are you feeling OK?” I smile benignly. “Fine, thanks. How are you?”

I’m not going to make this easier for them and tell them the truth of the matter: that I’ve just finished a major puking session in the staff loos, haven’t slept for three nights, and have boobs so heavy that I feel as if I need a forklift truck to carry them around. “Miss, I’m not trying to be rude (that’ll be a first then), but are you pregnant?” My form stops what they’re pretending to do and waits expectantly.

I put them out of their misery. To do them justice, they’re thrilled. And not because that means they’ll be getting a new form tutor, they assure me.

There sometimes seem to be very few moments in the life of a secondary school form tutor when you can really enjoy your form. Trying to get them to conform to normal school practice, such as arriving on time and being polite, are issues that seem fundamentally challenging to the teenage psyche and put you on a permanent collision course guaranteed to bring out the worst in pubescent tantrums. But once in a while you realise they are human; they break through that wall of teen indifference to remind you that, apart from their family, you genuinely are the adult in their lives who knows them best.

So we chat about the baby. Do I know the sex? (No.) Am I having a water birth? (No.) Will I ask for lots of drugs? (Definitely.) Can they baby-sit? (The jury’s still out on that one.) I tell them my baby can now officially hear things, so they need to be quiet during the whole of registration so they don’t upset it. Miraculously, they buy it, and creep around in that amazingly noisy way that only 15-year-olds trying to be quiet can.

I’ve been struggling to find some plus points about pregnancy so far. But sharing it with 30 overgrown babies is definitely one of them.

Gemma Warren is head of inclusion at a London secondary school. Email: gemmablaker@hotmail.com