Does your son think anything is going on with him?  If he doesn't then don't put the words in his head yet.  Work with his teachers etc...to support appropriate behavior etc...  If your son is aware that something is different with him then use his words, what is he percieving as different/going on and explain in very simple terms that people are different and learn different ways and need different support systems to get where they need to go.  Sometimes that means having special friends to talk to, or that spend the day with you at school, sometimes that means taking medicine to help you be the best you you can be.  Most of all let him know that no matter what is going on with him you love him and will be there for him!

Good luck!