3 year old resistant to potty training

My 3 year old son still isn't potty trained and will be kicked out of preschool if he isn't trained in 2 months.  It is a wonderful preschool program so I really hate to take him out of it.  My son will sit on the potty willingly only when bribed with some sort of reward and will only sit there if he doesn't actually have to go.  If he feels the urge to go while sitting on the potty, he will immediately get up and cry hysterically for his diaper.  While he is crying, he says "I don't want to be a big boy.  I want to wear diapers like a baby."  We threw away all of his diapers and put him in underwear that he picked out himself.  He treats his underwear just like his diapers and goes in them frequently.  He doesn't seem to mind if he is wet unless it runs down his legs.  He has been in underwear for several weeks now and hasn't made any progress.  He is very strong willed and is very resistant to the whole potty training process.   I know that he is physically ready to potty train as he can tell me when he needs to go and is able to stay dry for long periods of time.  

We've tried everything we can think of to motivate him but nothing works.  He has used the potty a few times but cried the whole time.  We rewarded him with praise and candy afterwards but that didn't seem to help motivate him.  Since he is so resistant, would it be better to just wait until he is ready to take the lead (and forfeit his wonderful preschool placement) or is there something I should be doing to motivate him?   I'm at my wits end and could really use some advice.  Thanks!

[Kevin Kennedy, Ph.D.]

Your instinct is telling you to relax the pressure and wait until he is more ready to tackle this developmental task. Follow your instinct. It won't be helpful to pressure him, and there really is nothing of a motivational sort that you can do other than what you've done - i.e., reward him for successful use of the potty. Since the pre-school setting hangs in the balance, it would be worthwhile to go for broke and have a chat with your son. Simply tell him that one of the requirements of the school is that children have to be able to use the potty. Let him know that the school staff and you folks would like him to stay at the school, but he can only do this if he uses the potty. Show him on the calendar the time frame involved. Now, to be honest, there's no reason to expect that this will necessarily be helpful, but it's worth a shot because of the 'stakes' involved.