8 year old still bites himself

Our son will soon be 9 years old.  Since the age of 4 we have noticed that when he is situationally anxious or excited he will reach his right hand up to his left shoulder so that he can bite on his upper right arm.  I've never seen actual teeth marks left behind nor has he ever bit anyone one else. He is very non aggressive. His teachers refer to him as a "gentle spirit" and we have never seen him be anything but kind. About 3 years ago I addressed this issue with our Pediatrician who just excused it as "something he'll grow out of", citing that he was perfectly normal. During first grade (he's now in 3rd) I addressed the topic again when his teacher inquired about him being tested for ADHD.  Her concerns were his inability to focus on the task at hand yet he always received good marks. His second grade teacher dismissed his actions as him being "deep in thought":)  This year the teacher commends him for being able to think "outside the box" and dismisses what little inattention exists as a brain break.  As a sidenote, since he was a toddler he has excelled in computers and anything electronic, both of which are learned at home.

However this is becoming a problem for him socially since his peers are now noticing his actions. Our son loves playing basketball.  I overheard a teammate mention after the game that our son would have got the rebound if he hadn't been biting on himself again.  Three of his teammates turned and confronted him as to why he needs to "always do that".  The look on our son's face was of surprise; I don't think he realized anyone else knew.
  As parents we ask him occassionnally for answers but he doesnt know why he does this.  We have even set up a "codeword" for him to stop. Our entire family has shown concern at one time or another and always inquire as to his progress.
As a infant/toddler our son never had a pacifier but he did carry a dearly loved stuffed "mouse" around in his teeth.  So much so that Gramma was constantly surgically repairing the nose of the mouse.  He still has a blanket that he wraps up in at night but otherwise he's just a normal 8 year old boy.

I don't know what to do next but the clock is ticking.  At some point one of these children are going to tease him or label him with hurt.  I would like to find a solution before it comes to this.  Most parent's concerns like this are in early developement years. What do I do now?  He fully understands what is happening but has not yet found the tool to prevent it.
Please help!

Thank you,
MommaDel

[Kevin Kennedy, Ph.D.]

As you can tell from your efforts to inquire of your son 'why' he does this behavior, he doesn't know. It's not as if he's making a conscious decision to do it. In that sense, it won't help to ask him why he does it. It's an automatic, habit response by now, very likely a tension-reduction knee-jerk response. If your son does display ADHD, the behavior you are noticing would not be associated with the ADHD. Might it be a tic - i.e., an involuntary muscle response? It is possible. Here  are two bits of guidance. First, request an evaluation by a pediatric neurologist. Second, re: the ADHD, if he is excelling in school you needn't do anything. If whatever degree of inattention he displays is not an impedimant to sound academic performance, it needn't be pursued. And, if your son does display a motor tic, the conventional pharmacological treatments for ADHD (i.e., psychostimulants) would not be good choices for him (though there are a couple of acceptable non-stimulant treatment s available).