I think getting away from some assholes in your school is a totally acceptable reason for considering the IB. You'll get more out of your education if you're happier while studying.
I'm afraid I've been out of full time education way to long to give essay tips.
This might be useful though. It's not exactly what you're after, but there's some general advice there that could be helpful.
Edit~
Just came across a
fairly depressing article on the subject of the IB's acceptance in America. Some people, huh?