Q.My 3-year-old son adores his 6-year-old brother and loves to imitate him, so I thought potty training would be easy.

Quite the contrary. We've persuaded him to sit on the potty chair a few times at home, but he lasts only about 30 seconds and then says that he's done. And as for using the big toilet with a seat -- forget it.

He is also reluctant to use the added potty at school. The teacher says that he cries when it is time to go and tells her to leave the bathroom door open. I told her that he may think the bathroom is too small, or that it's embarrassing to line up with 20 children, but frankly I don't know why he won't go.

If the teachers put him in underwear, or if he wears underwear at home, he holds in his urine until he has an accident. We tell him that's why he should use the potty but we don't chastise him; we try not to transfer my anxiety to him and we don't use incentives (which probably wouldn't work anyway). In fact, we haven't asked him to use the potty at all for the last past few months.

It's his total lack of interest that concerns me. Doesn't he know when he has to go? Isn't he ready to be trained? And won't my son ever get out of diapers?

A.Of course he will, but he'll probably be trained sooner if the teacher follows your lead.

Too much potty-pushing at school, and too soon, may be making it take longer to train your son, but so could other factors.

Even his basic nature could be playing a part. Some children train early; some -- especially boys -- train late. Some can hold in their urine or their bowel movements for hours, others cannot.

Children don't react to toilet training the same way, either. A sensitive child may insist on complete privacy in the bathroom; a very social one may move his potty to the kitchen or the playroom, just to be near his mom; and a child who is fascinated by facts will want to know exactly where his poop and his pee go when it's flushed away and to be told again and again.

Whatever your son's personality, he probably has some fears, too. Try to find out what they are and help him work through them so he will want to use his potty.

A child's developmental stage also may make your son wary. Many children resist toilet training between 18 months and 3 years because the need for independence is paramount at this age. Now he wants to decide what food he will eat, what clothes he will wear, where and when he should sleep, and when -- and if -- he should use the potty. If a child feels that he is given enough choices and enough respect, he will let his parents have their way about these and other matters. Sooner or later.

Or, as you suggest, your son may simply not be ready. A child can't be trained until he is physically, mentally, emotionally and socially mature enough to develop this skill.

You'll know it's time to put your son on the toilet if he uses his arms and legs well, puts his clothes and toys away most of the time, stays dry for a couple of hours at a time, watches his family use the toilet with great interest and sits on his own potty twice a day if you ask him.

If he's ready, success should be quick, especially if you adopt these diapering and toilet techniques, unscientific though they are. As long as your son is in diapers, use the standard design, because they seem to train children more easily than the kind a child pulls up. If he wiggles when you change him, stand him on a straight chair so he'll hang on with both hands and keep his feet fairly still. And when you think he's really ready to be trained, paint a target in the bottom of his pot, so he will want to aim more often.

For more on the subject, read "Mommy I Have to Go Potty!" by Jan Faull (Raefield-Roberts and Parenting Press; $13.95) and "Toilet Training Without Tears" by Charles E. Schaefer, and Theresa Foy DiGeronimo (Signet; $5.99). There is much to learn.

Questions? Send to Box 15310, Washington D.C. 20003, or to advice@margueritekelly.com