They wear it like a badge of honour, a measure of achievement. While most of us are trooping home wearily to make the tea or do the ironing before writing our reports late into the night, others settle down for a self-congratulatory gossip in the staffroom. These are the "committed professionals", vying with each other to be the last to leave.
Headteachers who define their existence through school often draw around themselves a group of acolytes with no home to go to who share their obsession. They sit there, setting the agenda, as the cleaners polish around them. The more balanced staff, often women with other commitments, are marginalised.
Of course, this is completely upside down. What we need are healthy, well balanced teachers who get the job done, not loners who don't want to go home. It is surely better to be productive at home than to faff around late at school. Being last out of the car park at night and then first in every morning doesn't make you an inspirational teacher. It just makes you tired.
One of the great things about teaching is the freedom it gives us.
We are recognised as professionals and thus permitted to manage our own time. A great deal of our work is individual to ourselves and we are able to do that wherever we are most comfortable.
Many teachers enjoy working at home, at their own pace, fitting it in with more important domestic issues. They can go home, deal with family teatime and then turn their attention to a productive and effective period of work.
They will achieve far more than they ever would if they stayed late in school.
There are many things that we need to do after school which require us to stay on the premises - meetings, phoning parents, sifting through the detritus of the day, and so on - but you can often choose what you do and where you do it.
You can go home at 3.30pm and be no less a committed professional than the poor time managers who drag themselves home at 5pm. Working at home is what we do in return for the generous holidays.
It is part of the deal. You can't do all your work - the marking, the preparation, the reports - in school hours. It just isn't possible. We signed up for homework. We promote it among our pupils because we believe that it is a Good Thing. So how can we say that it doesn't apply to us? Of course it gives us a long working week, and weekends too. But the compensation comes with the holidays.
Better to go home early and do it rather than to stay in school, wasting time so that you can get stuck in the traffic along with all those other workers who don't have the choices that we have.
Geoff Brookes is deputy head of a south Wales comprehensive