Sometimes I feel like its the parents that don't want their kids becoming friendly with my son because yes, he does occasionally get in trouble at school for not sitting or doing his work
I wouldn't assume that it is this. One of my son's good friends has ADHD and we do invite the child over to the house because DS likes him so much, but he is a LOT more work to manage at a play date than DS's other friends in terms of being very energetic, having more trouble following our house rules etc. He's a good kid at heart, and we do invite him whenever DS asks for him, but if I am tired or have other things going on, I would be more likely to suggest another friend when DS does not ask for this friend specifically.