Typically he sees somebody 'cheating' in a game in gym (which apparently they sometimes are in a not-so-big way and nobody else cares) or thinks someone is making fun of him at lunch (which sometimes they are, but sometimes are just being rowdy) and he gets upset and can't handle his emotions and sometimes ends up hitting. Recently he was suspended for hitting his teacher when she tried to intervene. My dear sister and her husband have tried a lot of things and are very frustrated. Nephew has been evaluated and found to be HG+ but did not meet criteria for any disorder (particularly ADD/ADHD).
Did they do an ADOS, or look at the possibility of autism spectrum disorders? These kids are often missed when they're gifted, because their language is so good; yet the social thinking mistakes you're describing are very characteristic.
They're going to try social skills group work as well as continuing individual therapy but the school is pressuring them to get a diagnosis and an IEP which they are resisting because they're afraid it will mean they will have to put him on drugs, which they are completely against. It's unclear what the school would even want to put in an IEP and my sister is afraid they will want to put him in some kind of class for 'bad' kids.
The school cannot legally recommend medication, let alone force it. The child is entitled to a free, appropriate, public education regardless of any decision about medication. There is no school record that follows a person through life.
As for the label: right now I'd bet that other kids are scared of your nephew for his unpredictable behavior. If there's something going on that can be labeled, that label is probably preferable to the informal labels that the kids are already giving him in their thoughts.
I would recommend cognitive behavior therapy and maybe Michelle Garcia Winner's Social Thinking curriculum. Those work explicitly on understanding how one's thoughts influence one's actions, and how other people think about what you do.
And they're worried that he might get expelled and that might go on his 'permanent' record and keep him out of other schools, public or private, and maybe even have to be reported when he applies college.
An IEP won't completely stop them from expelling him, but in our experience it gives much more leeway for appropriate correction of behavior issues and teaching the correct behavior. Highly recommended course of action is the IEP.
DeeDee