My daughter went through the same issues in grade school. She did not hit the staff but she had major melt downs and it was because the other kids would pick on her and the teacher would say she did not see it. Have you talked to the principle about this? I ended up taking her out and taking her to another school. I told the new school exactly what had happened at the old school and asked what their policy on that situation was. They told me they had a strict policy against bullying then told my daughter if she had any issues to let them know. She is now a healthy 14 year old and a perfect student. SO, I suggest you find a new school, and make an apt w/ the principle and have a talk w/ them before you enrole him.
I hope you have enrolled your son in another school. If his behaviour is good, then you will know that the previous school (for whatever reasons) was the problem. If his behaviour is bad, then you will need to find a third professional who can better guide your son while at school. I wish you the best ...