The key is to ask WHY these behaviors are happening. You’ve already noted one trigger, the environment — if it’s only happening at school then there’s something in that environment, maybe many things, that are triggering behavior.
Behavior is communication. What is his behavior signaling? Could be many things at school like sensory overwhelm (too loud, too bright, too chaotic, too fast…), social struggles, lagging emotional communication and regulation, etc.
I would request, in writing to the principle, an FBA (Functional Behavior Assessment). A behaviorist should facilitate this meeting and guide all parties to understanding the functions of the behaviors and setting strategies to address them.
And, if you haven’t, I strongly recommend you read Ross Greene’s “The Explosive Child.”
ADDitude Community Moderator, Parenting ADHD Coach & Author, Mom to teen w/ ADHD, LDs, and autism