Linnix13, I can tell you that beating someones a** dosn't work from my own youthful experience. When your looking at 15 to 25 it is not worth it and as you said it just gets bigger if you do go after him. By the grace of God I got lucky.
The secret here is if there is proof that he did this, you should get a lawyer and see if this knob can be sued. You can come out with money and the thug and his brother get a lesson that they will carry with them for the rest of thier lives.
When they go for jobs or a credit card or any number of things as they get older this will come back to haunt them. Think of it as the gift that keeps on giving. If they threaten you afterwards that causes them even more trouble.
Your teacher will, I'm sure, be safe. You are the one that took off on them, the teacher didn't say just go ahead. Also your teacher has a powerful union behind them.
Talk to a lawyer. They will tell you about the teacher being safe and what you can do. If he gets away with this your life will be h*ll as long as you are in school or he can get to you on the street.
As someone said this is an assault and he could well be charged by the police if you don't let it go to long.
If he is arrested the sound of the hand cuffs snapping shut will stay with him forever.
Steve.