6 year old son wets his pants

My six year old son wets his pants several times a day. I have taken him to the doctor a few times for this and they can't find anything wrong with him. I am at my wits end with it. What can I do? We potty trained him when he was 2. He controls his bowel movements and has never had an accident in his pants but he pees his pants everyday, several times. We have had him tested for uti's and they come back negative. He is in half day kindergarten and usually wets his pants after school but before he gets home. I tell him to use the bathroom every hour. Sometimes he will use the bathroom and 15 minutes later be wet. I am so frustrated! When I ask him why he wet his pants he says "I didn't". I am not sure if he really doesn't know or if he just doesn't wat to admit it.

[margypops]

If he is holding it at school maybe its because he doesnt like to ask to go, perhaps ask the teacher to remind him to go at school, it does sound as if it starts there.Does he drink a lot in the morning ?