I’ve joined a weight loss group. I’m not hugely overweight, but two pregnancies and an eat-chocolate-while-you-mark policy mean I can now fit into only one pair of trousers, so it seemed cheaper than buying a whole new wardrobe.

I’m not a great one for joining things - the last group I was a member of involved wearing a brown bobble hat and promising to serve the Queen - so I didn’t know what to expect. But I wore my heaviest jeans and ate a Mars bar on the way to give myself a sporting chance.

On arrival, I was ushered into the new members’ corner, where we filled out forms until group leader Cheryl pounced on us. She took us on a whistle-stop tour of the regime and handed out a glossy booklet full of oxymorons such as “a green salad makes a delicious starter” and instructions to “pig out” on broccoli.

“Have you been before?” I asked the two women next to me.

“Oh yes,” they replied happily. “It’s great - we join every January.”

I decided I liked them and sat next to them as we assembled for the meeting. It was like a very long and painful register: Cheryl read out names followed by the amount of weight lost or gained, which was greeted by clapping and the occasional small cheer. I tried very hard to become the sort of person who is motivated to eat more celery by sitting in a freezing church hall on a January evening, applauding because Linda’s lost half a pound.

Then Cheryl got out her positive pants. Last week, one of the members had admitted that she stayed motivated by having positive thoughts as she pulled on her pants every morning. This had inspired Cheryl to create some cardboard designs of her own, which she had laminated for the meeting.

I had been teaching characterisation through body language that morning and I couldn’t help but be impressed by Cheryl’s dramatic range. When the news was good, her head bobbed up and down enthusiastically; when someone was struggling to give up Coco Pops, she did a compassionate head tilt. She was in her element when it emerged that someone had put on weight, expertly probing them to get to the root of the problem.

When Bill (1lb gain) buckled and admitted to eating his slimming soup with a side order of baguette and butter, there was a gasp (in the diet community, consuming crusty bread and butter is the equivalent of doing lines of cocaine). A broken man, Bill muttered a thank you as Cheryl gave him a pair of positive pants and a conciliatory round of applause.

Although they might not impress Ofsted, Cheryl’s teaching methods are surprisingly effective. Only this lunchtime, I was about to tuck into a large chunk of baguette and butter of my own when the thought of Cheryl giving me a sad-but-knowing head shake while handing me a pair of positive pants stopped me in my tracks. I had an apple instead.

Jo Brighouse is a primary school teacher in the Midlands