Son does not play well in groups

My 6 year old son plays well when playing with one other child, but often does not play nicely in groups. His teachers do not think he has a social problem and have not raised any issues with us in this respect.  However, I have observed him in the playground and at social gatherings and am unsettled by what I see.  He gets verbally aggressive, spiteful and occasionally a bit physically aggressive.  When he is like this he does not listen to adults and is like a stranger to us because his behaviour is so out of character.  It's almost a trance-like state in that he doesn't respond to instructions or even make eye contact when we remonstrate with him during the "episode". He becomes defiant and behaves as if the whole world is against him but at the same time he  can't disengage.  It's as though he doesn't like how he's feeling but is unable to understand it or do anything positive about it.  He becomes confrontational and it's like a sulk in which he is taking out his resentments on the other children. Afterwards he doesn't see how he was wrong and says the other child made him behave that way.  This is disturbing behaviour because he appears to be a sensitive and loving child, often doing and saying kind and thoughtful things.  He likes to have friends and often wants to invite schoolmates for playdates.  Not all playdate invites are taken up.  He does not get playdate invites and his invites are not reciprocated.  He isn't invited to parties unless the whole class is invited.

[specialmom]

Hm.  Well, I can see your concern.  On the surface everything seems fine and teachers are not picking up on a problem but his behavior on the playground is clearly having an impact on his peer relationships.  It is hard when issues are not blatent and getting the attention of others -------  although the alternative is no fun either.  But I too would be concerned mainly because his behavior is setting up a situation in which others are not wanting to be friends with him.  They might have gotten along great one on one but that never comes to fruition because it gets ruined with his mean, bossy behavior on the playground.  They don't want to hang with him because of that interaction.  I get what you are saying completely.

I would look at it as he really does have a social issue whether the teachers feel so or not.  I would work with him on friends skills.  This means dialogue at home about what it means to be a good friend.  As he says he really wants to be-------  perhaps he will be motivated enough to make some changes.  I would tell the teacher that while he is not having outright issues in school that you feel he is because he seems to have no real friends outside of the school day.  So let her know you are working on some things.  I'd see if you could come and be a playground helper to observe.  This time should not be spent interfering in what he is doing but getting ideas for how to help him.  If you see that he is bossy.  Well-------- you work with him to say that there is a rotation for choosing what they play.  Let him know that he can perhaps choose on Monday and that is it for the week.  Then Joe chooses on Tues, Sam on Wed, etc.  This probably sounds odd but my son who has sensory integration disorder and some social issues works well under rules to follow.  If he knows that when we have a guest at our house that they get to choose what they do--------  he'll go with it vs. if I haven't set that up, there is much squabbling.  I think that you can then try to find mother's of two or three other boys that you are friendly enough with that you can be honest.  Tell them that you are working on somet things.  And meet out at a park.  Tell him ahead of time that if he is bossy, mean, or physical with anyone------- play date is over and you are leaving.  Then set the date------ and see what happens.  You stay close by and intervene to say this is your warning.  Then if he continues, it ends.  I also think it is a good idea to keep the one on one play dates up with these kids at school because if they go well, they are more apt to cut him some slack when those nasty group dynamics take place.  
How would he do in something like soccer where he is in a group but not the boss?  What about cub scouts?  
good luck