My girlfriend is a teacher and this is what I have gleamed off of her.
You need to want to teach. Teaching is a mixture of, in no particular order;
1. Imparting of knowledge.
2. Administration.
3. Crowd control.
You have to like kids, this is the bit that put me off of teaching. I agree that you do not get as much holidays as people think due to preparation time. Plus the hours are long. My other half usually arrives to work at 07:00 and leaves 17:30 at the earliest frequently not until gone 18:00. School is shut at 19:00 but most evening involve marking in front of the T.V until bed time + work over the weekend so summer holidays is the only real off time.
Pay is quite good I think, maybe everyone on STW are all bankers but I think the money is pretty good. If you are complainant you can rise up very quickly. Five years can get you HOD which in London is £50k. Your wages will still increase further, there are a fair few of teachers on £60k +
You can be lucky though and get a cushy job, my girlfriend works in a rough S.E London school, hence progression is faster and there is more work. Her friend works in a school in Stirling, and get home for 16:30 most days and starts later, but she has been teaching for 2 more years and has not progressed as much.