can a teacher put his hands on a child? assaulting the child inappropriate way?

my son is a 6th grader and the gym teacher assaulted my son at lunchtime also another person was present when the assault happened -teacher's aid. My son went to the main office to call me and the teacher followed him so he wont call. The principal and the office staff seen the gym teacher assault my son,no one in the office including the principal said anything to this teacher. My son was trying to call me and the teacher grabbed his hand again so he wont call me. at the end of this incident the principal had to say let go of my son 4 times before the teacher actually let him go. Since 4th grade i been having issues and between the school and board of education they have not done anything when I go to the school and give a complaint about a teacher etc. On Wednesday was the end of it. I need to look for assistance on this matter. I been trying to handled on my own however it has not worked. I need some guidance in what to do. I went to board, called dyfs and police department.