No symptoms except for hand flapping

My 11 year old son continues to "hand-flap" (has done this since he was very small), particularly when it's been a busy day, or overstimulated.  He seems to need this to "chill out", and consciously says he just needs to do "Action Boy" (this is what we have called it) for a couple of minutes each day at some point.  Other times, it could be brought on by something like water patterns (his grandfather has a boat, and he loves watching the water around the motor move).  He usually (but not always) has a pencil or other object in one hand and the alternate hand hangs out.  He flaps both, and looks much like a musical conductor while doing this.  

I have researched Autism and Aspergers, etc., but he literally has no other symptoms of anything that I can find except for this hand flapping.  Since he seems to get more out of it in a soothing, wind-down way, I hate to make him feel that there is a medical problem if there is not.  He is very well-adjusted, he has many friends, interacts well, does well in school, spoke very well at an early age, and is otherwise "normal" in literally all aspects of life.  Except the hand flapping!  We have been thinking it would eventually "run it's course", but he continues it, without embarrassment!  We have tried talking with him, and he understands that he should try not to do this at school or in public for a couple of reasons.  First, it distracts him and "takes him away"  and second, he's at the age where he will likely be made fun of by those who don't already know him.

Could there be some other reason for this?  Should we be worried about this?  
Thank you for any advice!

[William L. Holcomb, Ph.D., BCBA-D]

I am not sure I will be of much help, but I thought I would just mention that if you are quite sure that your son is not engaging in any of the other behaviors that would be indicative of an autism spectrum disorder, then I agree with you that this is an unusual behavior, but perhaps harmless.  I was particularly struck by your comment that he appears to understand that it is not appropriate to do this is front of peers and teachers.  At your son’s age, peer relationships and the complexities of the social environment that surround them become increasingly important.  If other children make fun of him for this behavior, you may wish to ask for advice from his school guidance personnel or a trusted teacher.  Otherwise, you may wish to consult with a behavior analyst about ways to teacher your son more socially acceptable behavior than the overt hand flapping (for both when he sees something he likes or needs to calm down).  Every parent is bound to be worried about anything that is “different” about their child.  If the behavior in question does not interfere with your son’s life in any way, perhaps it is not worth worrying about.  One final comment: if you notice that the behavior occurs more frequently in your presence (or under any particular set of circumstances) that would be worth exploring with a behavior analyst.  You provided a couple of examples that seemed quite disparate; for example looking at a specific event (i.e., the water surface patterns), but also that he needs this to “chill out.”  Among other factors, you would want to make sure that there are no social consequences that might be maintaining the behavior (e.g., attention from you or others when your son flaps).