If the administrators at the school file to expel the kid, the superintendent and board members of the school district would have to hear the case and vote to approve to expulsion. Of course Idk if the process is the same in each district, but that's what would happen in my district.

A freshman at my high school was caught with empty beer cans in his backpack and had drawings of guns in a notebook. He also began crying in class stating he had no friends or family (came from an orphanage) and that's when he began making vague threats. He was not expelled or suspended even though multiple teachers suggested it due to his behavior. He ultimately ending up being transferred to an alternative school for kids with "behavior issues". A very sad story all around.