Now, in my foolishness, I have run the London Marathon. It hurts. Why should anyone want to go through that pain for the distinction of finishing a race in 9,723rd place. I’m so stupid I ran it again and, before finally learning the lesson, a third time too.

So I reckon I have earned the right, through the battle-scars of blisters and sore nipples, to accuse teachers of masochism.

Is this not the same profession which tells us they are working an average of 53 hours a week? The same profession whose representatives at the Easter conferences told us they were so exhausted they dreaded Sunday nights? How is it they have energy to spare to pound the streets?

Now I am not so masochistic myself as to risk the wrath of teachers by suggesting they do anything other than work hard. Nor would I dare suggest that if I had 13 weeks’ holiday a year I could trim at least five minutes off my personal best marathon time. But what makes teachers, when they’re exhausted after a day in the classroom, pull on their trainers and put in the training miles needed to complete a marathon?

Is it simply that all 1,849 were PE teachers who are so fit they could run the marathon without extra training and then jog off for a game of football in the afternoon?

Or maybe it is simply that the miles of school corridor teachers walk in an average week is training enough? Or, taking a more anthropological approach, maybe it is that, as David Attenborough might put it, “the natural habitat, and daily struggle for survival of the teacher species has equipped it with a naturally high pain barrier”.

So perhaps after an afternoon in the chemistry lab with 9S, leg cramps and searing lungs barely register on the pain scale.

But no, I have a quite different theory. Teachers really are masochists. What other group of people would endure being blamed for all the ills of society in exchange for long hours, poor working conditions, and spending the day locked in with teenagers?

I mean teachers can’t even make the afternoon go faster by looking up their avourite websites on the office computer.

Further evidence of their masochistic tendency is exhibited by teachers’ fondness for sacrificing their holidays to attend Easter union conferences. Here, they can repeat the arguments and whinges that have sustained them in the staffroom the rest of the year.

And have you noticed how teachers - rather like police officers - are never off-duty? Meet a teacher at a dinner party and you can bet that the main course will be accompanied by talk about the national curriculum and they’ll be onto league tables by dessert.

Eavesdrop on two teachers in the pub and they won’t be talking about football or gardening. Oh no, they will be discussing their pupils, this year’s coursework or their new timetable. Do you remember the thousands of primary teachers who splashed their way through the ridiculous “sinking and floating” science SATs - even when they didn’t believe in it?

Now, if you were being reasonable, you would say teachers are too conscientious for their own good, they believe rules matter and care about their pupils. Indeed, I have long suspected that behind their world-weary cynicism there’s a deep core of caring. But this latest evidence from the marathon has made me reassess. It’s clearly much simpler: just masochism.

That is why the Channel 4 series Teachers is so unrealistic. Its main character is an amoral, selfish young man whose conscience has been surgically removed, and his male colleagues are infantile and oafish. You might have thought teachers would be furious at this portrayal but I’ve found that most of them love it.

Why? Because they would like to see themselves as free-wheeling, uncaring individuals but, deep down, they know it’s just a fantasy. It’s the same with journalists. We’d love the public to think it’s all gambling, boozing, and fighting just like in Drop the Dead Donkey when, in fact, it’s a bunch of hacks poring silently over news releases and flickering computer screens.

So what do you do if you’re a teacher, with a masochistic streak, and you have a void to fill during the holidays? Why, you train for the marathon of course. Top up the pain. Tell anyone who’ll listen how awful it is. Smile bravely as you cross the finishing line. What could be better.

Mike Baker is the BBC’s education correspondent