Some fabulous advice on the social skills issues above. I'd just add an additional consideration on the ADHD issues.
On the one hand, kids with ADHD tend to have notable executive function defects, and these rapidly become more problematic (fast!) as they approach middle-school grades. An accelerated kid who's well-behind grade level function may have a brutal time trying to manage expectations of an even higher grade.
BUT - a huge but - it's also really important to remember that ADHD affects our ability to control where our attention goes. It makes it extraordinarily difficult to keep attention focused on work that is boring (or hard, especially when other Es are involved). My kids are far more capable of staying focused on work that is challenging and engaging. And far more willing to work through the pain of their other disabilities, and battle through the hard stuff. The only thing that triggers the ADHD worse than make-work, is make-work that still places high demands on their LDs (e.g. no conceptual challenge but large output requirements).
So it's really important not to get caught in the usual teacher trap, which is "fix the behaviours *before* you can get interesting work". Interesting work tends to be an essential need to fix the behaviours. Which is not to say accelerate is necessarily the answer. The decision requires some tricky untangling of cause and effect. How can you best get him work at an appropriate level, while also best supporting social and emotional development? What changes can help in deficit areas, and what will exacerbate them?
