Help!!

Okay I'm getting desperate, or really impatient maybe...so I'm looking to all of you for suggestions...and not just from people with kid's-from others too, if you have any ideas for me....Aiden is being a very naughty potty trainee.....He is PERFECT and DRY at the sitters ALL day long! He sits on the potty like a nice boy, has not had an accident in weeks...but when he comes home he pees and poops in his pants. There is no attempt to go, he'll tell me "Mommy I"m peeing" or he'll just look at me with a funny little smirk on his face, sometimes I can get him on the potty but will he go? Not a drop! Tonight, we were playing a game on the computer and I told him we would go potty o the potty chair and then get in the bath, it was shortly after supper time....so he runs to the living and starts collecting his random toys that he wants to bring in and comes back totally soaked, he completely peed in his pants. What do I do now? He's only wearing underwear, I've used stickers, bribes, I'm getting to where I'm sitting him down in the chair for a time out when he pees....He obviously knows what he's doing....but I don't really want to "punish" him for peeing but I think since he knows what he's doing maybe he should get some sort of a punishment...the part that frustrates me is that he seems to know what he's doing at the sitters but not a clue at home, and she doesn't do anything special...I know his little buddies are mostly all potty trained so that might have something to do with it, but why won't he bring that knowledge home is beyond me...other than he's 3 and is a stinker.... anyway, can anyone help?? any suggestions or thoughts on the matter would be much appreciated....thanks!! :)