7 year old exposing himself at school

Last fall my son exposed his penis to 3 kids at the end of his Phys. Ed class.  I sat him down and talked to him about privacy, and how inappropriate this behaviour was.  I let him know that I was disappointed in his behaviour but I love him very much.  He was grounded and I felt that he was better informed and sorry for not thinking before acting.  
Today (April) my sons Phys. ED. teacher called me to let me know that a boy exposed himself to my son and another boy.  Upon further questioning is seems that my son and the second boy told the third boy to show them.  I'm concerned that this could be a sign of something deviant.  He is currently being evaluated by a Child Psychologist for ADD.  Could this be part of his ADD?  Should I handle it the same way... will the results be the same?  

[littlehill]

Have you talked to him about the Birds & the Bees yet? It seems like they just think it's funny, which I don't get at all. My 5 & 6 year old were doing the same thing as well as ther 5 year old step brother. I got this great book called "It's NOT the Stork" by Robie H. Harris, sat down & read it with them, once they realized there private were PRIVATE they stopped doing that.

[Sandman2]

   Well, if it was deviant behavior I think it would happen more than twice every 7 months.  I do think it is kinda normal for this age.  You always wonder whose idea it was and who was tagging along.  It could be a part of ADD.  It could be two guys making another guy feel like an idiot.  I would definitely remind him that just as he should not be showing his privates, you don't ask another to do that.  I would think the fact his PE teacher noticed would be enough to quash this in the future.