Our DS said he would start using the potty when he turned 4 -- but once his 4th birthday came, he kept delaying it -- he said he just wasn't ready...finally at about 4 and 2 months I told him he could get Jelly Car 3 (i am not a fan of jelly car) if he started using the potty -- he immediately dropped everything and ran to the toilet (but didn't have to pee) -- so he drank a bunch of apple juice until he had to go. That was it. Video game - like ABQMom. Then...he he was stuck on pull-ups (which he didn't need). We finally got rid of pull-ups at 4.5. Phew! But this is a kid who has a shoe issue too -- he is only on his 3rd pair of shoes ever (refusing to wear new shoes).
