I catch the new supply teacher as she’s leaving at the end of the day. “How did it go?” “Great,” she says. As I look at her shiny eyes, paint-splattered shirt and flushed face, I know she means it. “Four half-drunk cups of tea,” she adds.

I know how good it feels to be a supply teacher: coming in, doing your job, then walking away at the end of the day without any planning, politics or post-mortems.

I used to love it - you’re always welcome. I used to feel like a superhero turning up at a desperate school to be greeted with: “Thank goodness you’re here, you don’t know how glad we are you could come.” I considered wearing a superhero-type vest at one point, with a big S like Superman for “Super Supply”.

A good supply teacher always comes prepared: swimming things, sports things, spare tights (for women - or Superman), coffee in a little Thermos, and a lesson, a story and half-a-dozen songs up your sleeve. I quickly learned not to forget swimming things. While most special schools have a store of spare costumes, the only one that usually fits you is the floral number with the frilly skirt and the see-through top. Oh, and don’t forget a warm coat. Make no mistake about it, whoever you are covering, and whatever it says on the rota, the supply teacher is always on play duty.

We choose our supply teachers carefully. Each class is staffed by a team of excellent teaching assistants, as well as the teacher, and are very able to run the day themselves. In fact, they would often rather do this than have a supply who doesn’t know what they are doing, winds up the kids (just by being a new face) and eats all the biscuits.

We are lucky as we have a couple of tried and tested supply teachers. They don’t seem to mind if we book them for music in the nursery class, and greet them as they arrive (in dungarees with a guitar strapped to their backs) with the news that, in fact, they’ll be doing messy play with jelly and blancmange in the morning and the “citizenship group” tour of the law courts in the afternoon. Let’s hope our new supply teacher manages to do as well. I’ve a feeling she will.

Maria Corby is deputy head of a special school for pupils with severe and multiple learning difficulties. She writes under a pseudonym