Nearly all the teachers I know work over and above what is actually expected of them.
And London (where I happen to know teachers) is one of the most expensive places in the world.
If they are paid well - so they damn well should be. I entrust them with my children for huge chunks of time, and expect them to educate, support, discipline, nurture and like them.
Not a lot of jobs more important than that, IMVHO.