I agree w/ Neato. Perhaps it's not the kids are excluding him, but he's excluding them b/c he has no common ground with them. If he sees them as "childis" or "acting their age" that might be case, unless he's just saying that as a shield to rejection. You say he plays well w/ neighborhood kids of all ages so that is a great sign. Perhaps there was one significant event which occurred in the classroom which has cause the current situation?
I would definitely seek a 2nd opinion on the ADD, given that meds are being used, and would also most definitely seek gifted eval from someone experienced in gifted issues.
good luck!
