Fights at school

Why do students fight at school knowing the consequences? Students fight at school because some people just don't know how to control their anger problems or they just don't care. Some peoples tempers just need help and they don't try to prevent their tempers from going out of control. What should happen to a student that injures a teacher? I really do strongly believe that if a student injures a teacher they should not be allowed back at that school. They would have to go to a different school to finish the school year. Its that serious of an issue to me, Teachers are here to help and benefit your future and if you are stupid enough to injure one that you just don't worry about coming back.