inappropriate touching of genitals

I am a special needs teacher.  I have a student that was diagnosed with PDD.  He puts his hand in his pants and touches himself repeatedly.  There doesn't seem to be a specific time this behavior occurs.  He doesn't appear embarrassed when asked to remove his hand, however, after just several seconds he is doing it again.  Any ideas on how to modify this behavior?

[momforever]

My son has PDDNOS (along with a long list of other 'd' diagnosis(s)...this is a very huge problem for him - and others.  I am relieved to hear of other examples of this. I hope someone out there may have some answers. My son is now 11 and the repercussions of this kind of behaviour at his age are scary to contemplate. He does become very angry if he thinks reminders to stop can be seen or heard by others. This anger can escalate to aggression. An incident at school involving an assistants 'reminders' led to a two day suspension last year. Like your  student, my son seems unable to stop this once he gets focused on it and reminders often seem to make it more prominent.

Any suggestions from others would be most welcome!