In reply to TobyA:
My wife's the head of a prep school. She alternated between private and state for years, keeping her hand in in both, and then became a head (after a year as a deputy).
She disagrees significantly with Gove, who seems to think that teachers who don't know how to use an apostrophe can nevertheless teach Middlemarch. Sadly she had the microphone removed before that little discussion could really get going. There would, however, appear to be growing recognition that improving standards requires teachers who are themselves better educated, which is where it gets a touch difficult.
I would say be very careful about what you want and where you want it to go. Nothing would induce my wife back into the state sector now (famous last words, maybe). Furthermore, one of the reasons she became a head was that she was too expensive as a teacher in comparison to NQTs. Budgets seemed to have the upper hand over experience and ability. Consequently, if entering teaching later in life, perhaps think on what you might want in x years' time and how it all stacks up.
Effectively, she runs a small business, that's subject to external inspection (with one day's notice), with c.400 stakeholders, 200 direct 'clients', 40-odd staff and a >£2m turnover. Add to that, 16-20% of the customer base needs to be replaced every year.
She gets to deal with the police, social services, traffic wardens, employment tribunals and governors among many others. She's 'sales manager' for the school - if she doesn't get enough children in though the doors every term/year (and keeps them), the school will start to struggle. If the parents aren't happy, the word gets round really fast, but good news travels too.
Frankly, I don't know how she does it, but the school's full and there's a waiting list in every year group. It's certainly rewarding, but exhausting. She still teaches a bit too. On a daily basis, staff are the most trouble, followed by parents and then kids.
Finally, have a look at the TES and see what jobs there are that appeal and might suit.