This reply was originally posted by user Benine in ADDitude’s now-retired community.
My son does this too. I imagine he zones in on his own thoughts or micro-projects for half a minute, then when he looks up the others are gone. It’s not that he is uncomfortable with the group, just that his mind is not thinking about what the other kids are doing all the time. He really likes playing with other kids, but his mind sometimes wanders away and finds other ideas to occupy itself with.