MNMom, he has 4 months under his belt of a new social skills group and he is trying out his new skills of saying hi, starting and continuing conversations, etc. They sometimes work, sometimes don't and it is VERY stressful for him.
Ohhh. Having read this, I think I understand why these behaviors have been surfacing lately. This is still a fairly new skill for him. Could it be that his attempts seem awkward to others and they react in ways that trigger your DS? Have you gotten any feedback from his PE/art teachers about how he's doing socially for the few minutes leading up to his behavioral problems? I'd definitely question this, since it seems likely that there's a particular child or situation that sets him off lately.