However, I am uncertain whether the parallel with plumbing was an April Fool’s joke or a serious point. Some teachers might argue that they spend a disproportionate amount of time chasing other people’s little shits through a system too confined, outdated and constricting to allow their easy passage from beginning to end. On the other hand, comparing teaching with plumbing, even in jest, provides an ideological foundation for aspects of educational restructuring that are not at all funny.

Mr Wilby suggests that teaching, like plumbing and unlike law, does not require a body of esoteric knowledge. Sewage! Sixth-form teachers have to transmit considerable knowledge about and enthusiasm for such arcane matters as biological naturalism, European electoral systems (delivered, naturally, in German, French, Spanish or Italian), genetics and calculus.

Primary teachers are merely required to know everything. We all have to understand the psychology of learning, child and adolescent development, and motivating and managing others. The idea that we have skills but no special knowledge renders us interchangeable, much as plumbers or hairdressers are. If the toilet is blocked, any good plumber can fix it. If I have split ends, any competent hairdresser can sort it out. If the head has a teacherless class, any teacher will do.

I know linguists who are teaching secondary maths, and all sorts of people who have been roped into teaching languages they can barely master themselves. Colleges are increasingly maximising efficiency by deploying full-time staff across a wider range of subjects. Some students will inevitably miss the opportunity to be inspired by a passionate and knowledgeable teacher, because their class is fronted by someone who has classroom skills but little specialist knowledge, and no enthusiasm for the subject they are “teaching”.

This makes no educational sense. Whereas a plumber can stand in front of any toilet and have a good attempt at solving the problems posed by it, teachers have more diverse - dare we say, differentiated - abilities. This is necessary because the classes we face are so different. I could not be a good primary teacher, secondary maths teacher or sixth-form physicist. I would rather ferret around in the darkest recesses of other people’s loos than enter a class full of teenagers with behavioural difficulties. My craft may be extendable, although I doubt it. My knowledge isn’t; it wobbles in various key areas.

Yes, let’s see ourselves as skilled workers crafting a better future for young people. But let’s not be fooled into believing that we are units of equal value to be slotted into any available gap in the timetable.

Jo Lally

Jo Lally teaches critical thinking at Havant college, Hampshire