I'd suggest you take it to court if you have a witness, other than the guy who broke the phone of course.
Sue him for the cost of the case and repair bills, cause the case will likely be as much as the repair bills.
Though, leave this as a last resort, check up with your school to see if they can't handle the situation, would be much easier than filing for a lawsuit.
As for future cases, be sure to pick up something to protect your phone, you might not have broken it before, but there is always a first.
Take this time as a lesson for the future.
Wish my parents would learn that, they've shattered / broken at least three phones, phones they've barely used.
Though, I imagine it's the person not the phone. I've dropped ones I've been using three times before, never broken them once.