4 1/2 year old won't poop in potty!!! Help me please!

I have a 4 1/2 son that refuses to poop in the toilet.  He goes to another room and poops on his self. He'll even go in the bathroom and still will poop in his pants.  During the day I put him in underwear and he very rarely pees on his self.   When he poops on his self he may not even tell me.  And when I smell it I ask him why he didn't go to the toilet and he   tells me he didn't want to.  He knows he's suppose to poop in the potty and he does but about once a month.  Then when I get angry with him and start to yell he starts getting hyper and dancing around and laughing about it. He sometimes makes me chase him just to get him cleaned up.   I have explained to him that all his friends us the potty and he doesn't seem to care.  I told him he needs to start pooping in the potty in order to get to go to kindegarden in August.  I already think he has ADHD so I don't know if that has something to do with it.  We are in the process of getting him in therapy for behavior issues but I'm just at a lost of what to do anymore.  I don't see it getting any better....ugh.  I'm embarressed and feel like a bad mother.  What can I do????

[AnnieBrooke]

If you think this is part of ADHD, ask the therapist about it.  If you think there is any possibility he really doesn't know when the poop is coming, read up on encopresis.  He might have a dysfunctional bowel.  (Encopresis is characterized by kids not having the urge, the poop just comes on them without warning.  If it's that, no amount of anger or scolding will help, he would need to see a pediatric GI person, or at least a well-informed pediatrician).  You can find good explanations of it online.  Good luck.