S.K.
Hi V.,
My 3 year old had some issues regarding his personal space at preschool. He would get angry and yelled a lot at the other kids. We found that role playing worked very well. I would suggest a "nicer" way of using his words and he eventually began using them at school with his peers. I think role playing a specific situation gave him the knowledge and confidence to correct his behavior. His teachers were also a big help.
Also, be assertive with the principal. Continue to seek his time so he knows you're truly concerned and want to fix the situation.
Don't give up and good luck......this too shall pass.