When my oldest son was in 6th grade, he was assaulted at an afterschool club. The boy who assaulted him was banned from the club for the rest of the year but I don't know if he had any other punishment. They tried to suspend my son for 3 days along with another boy who tried to intervene to help my son. When they told me that, I went ballistic and went to the police and filed a report. My purpose was not to get a 7th grader arrested but imagine my shock when the police told me that the boy's name was not unknown to them!
I then called and demanded a meeting with the principal. The first thing he said to me was "Just because you're a lawyer, did you have to go to the police?" I replied "I went to the police because I'm a mother, the fact that I'm a lawyer just means that I'm not scared of you or them"
My son wound up getting a 1/2 day in school suspension which created another problem (LOL!) because my son decided he loved ISS so much that he would rather be there than in class!
My opinion is that if the other boys are 6th grade or above, I would go to the cops. As for continuing PE, my kids would be happy to be out of it for the year so I wouldn't push for it but if your son wants it, you should demand that he go back in.
Good luck.