A.V.
Sounds to me like this is a bully problem and not an ADHD problem and you need to address it as such. What is the school's bullying policy?
And even really smart kids do dumb things. Like a young lady who nearly didn't graduate because she failed English for lack of assignment completion, but won the literacy award. If he has no missing assignments, then what is she concerned about? Be specific. My SD had a teacher that hated her, the VP was involved, etc. Her final was graded as an F. We called foul and the school hand graded it. She earned an A. Sometimes there are true conflicts, but you can't just go in guns blazing.