Dr. Greene, my four-year-old son has a history of withholding bowel movements. He's trained for urine just fine but refuses to poop in the potty or toilet unless under extreme duress, and after a few weeks of trying, we've given him his diapers back. He's now happy to poop every day, hence avoiding the anal fissure problem, but what keeps kids from pooping in the potty? Being four and in Jr. Kindergarten, this is a concern for us. Any ideas??

One of our advantages as parents is our size. If we need to get our preschoolers into our cars in a hurry, and friendly negotiations have failed, we can still scoop them up and slide them in. If two preschoolers are fighting, we are big enough to gently but decisively separate them.

But in the arena of helping kids to poop on the potty, our superior size affords no advantage. We can teach them how to do it, we can tell them when to do it, but we can't just make them do it. They are able to simply decline. The longer they refuse to comply, the more frustrating and embarrassing it becomes for us as parents (especially if there is peer, or in-law, or school pressure!).

We hear that if we just wait, they will learn. We're told that no one graduates from high school in diapers. But we wait, and there is no progress.

We throw our efforts into getting them to use the potty, sometimes to the point of "extreme duress," but that tack doesn't work either. The more we try to force them to use the potty, the more they can resist. And they will win.

Children don't have to poop on the potty unless they want to.

The good news is -- they want to!

Children have a deep, urgent desire for growth and mastery. They would love to be able to poop on the toilet like their parents, like their teachers, like their friends. This longing is profound, and will win out in the end.

What could be powerful enough to block this freight train of progress?

There are several answers to this question, but in your son's situation it sounds as if he is trapped in what I call the D3 cycle (discomfort - dread - delay).

Children can enter the D3 cycle at any point. Sometimes it begins with an uncomfortable experience passing a hard stool created by a change in diet or a brief illness. Sometimes the starting point is simply the fear of sitting over the gaping hole in the potty to poop. Sometimes children are engaged in playing and choose to ignore the urge to poop, holding the stool in just to delay interrupting a vitally important game.

Whatever the starting point, they end up having a painful experience. When the next urge arrives, the child decides to delay pooping in order to avert what happened last time. The longer he delays, the firmer the next stool becomes. When he finally does poop, the event is even more uncomfortable -- confirming his fears. What he dreaded was true!

He vividly learns from this experiment, but it's the wrong lesson. So next time he is even more determined to hold the stool in. Discomfort leads to dread; dread leads to delay; delay leads to discomfort. The rectum stretches internally so that more stool can be held, and soon urges to defecate are not often felt. The D3 cycle becomes a powerful trap. Progress is derailed.

The D3 cycle must be broken before moving ahead with potty learning.

Sometimes going back to the "good old days" of using a diaper can break the D3 cycle. The child relaxes, the stools get soft, and the tension disappears. Stools again come regularly and without protest. It sounds as if this has happened already for your son. This solution runs the risk, though, of forming a very strong connection in his brain: diapers are good, potties are bad!

Sometimes modifying the diet can result in soft enough stools to break the D3 cycle.