J.L.
I agree with below, if you know that he is regular and does the "poopy" like clockwork at a specific time make sure you get him to sit on the potty during those times. Unfortunately, it is also about when they are ready...My daughter took forever to potty train and now just recently within a two week period my son who just turned three is completely potty trained day and night...Go figure!! Just be consistant and positive encouragement. He will do it when he is ready.