He sounds like he has a lot of positives.
He's got a very high IQ, and he's in sports, and is keeping up in school although he fails some tests?
If he has ADHD, I think you can expect him to lose a book here and there, and a bus pass.
It sounds like he is also hard to be around because of his defiance.
On balance, it sounds like he is doing okay in school? What sports does he play?