When something similar happened to my son when he was in the first grade, we had to take the matter to the police, involve DYFS and sue the school district to ensure that both children were protected. Mainly, I was worried about my son considering that there was violence and denial on the part of the school. So my son is 10, still in therapy (huge peer trust issues), we've changed schools, settled out of court and the other child is now out of state. But this is not an easy thing. If you want to talk about it more, please feel free to PM me. I am so sorry this happened to your son and your family.