Potty training and the 4 year old

I have a 4 and 1/4-year old boy who almost always successfully wears underwear -- until he has to "poop".  When he feels this urge, he insists we put on a diaper, and when we've tried refusing, he becomes constipated.  

This has been the situation since he was two and three-quarters, at which time he began to urinate in the potty.  He otherwise is quite well-adjusted and smart, and his life is FAIRLY consistent.  Any suggestions?

[Kevin Kennedy, Ph.D.]

Dear Beth,

It's probably time to bite the bullet, so to speak, and push your son to master the toilet training. To do this, of course, you'll have to stop cooperating with his request for a diaper. Do this planfully, in a straightforward and casual manner, establishing a reward system for successful use of the toilet. Consult with your pediatrician about a regimen to use to safeguard against constipation. Once your son successfully uses the toilet, without discomfort, he'll probably proceed fine.