[jeffgrant]

I'd go and talk to him first and foremost. In my opinion, the goal is to eliminate the behaviour, not catch him at it.

A quick talk outlining the concerns might put a scare into him and make him think twice before doing anything else. Right now he's probably doing it because he thinks he can get away with it, and he's trusting the kids to not squeel on him. If you can get him to think that the kids ARE squealling on him, then he's probably not as likely to do it.

I'd also have a quick talk with your son as well... and just let him know that you trust him to do the right thing, etc. Kids can (pleasantly) surprise you sometimes.


$0.02

EDIT: I'd also talk to his superiors, and raise the issue with them. If you tell them that you've heard rumours, they'll more than likely REALLY make sure it doesn't happen.