My son was the same way, and one of his teacher told me to buy him his favorite toy and put it in an unreachable place where he could see it, and tell him that he can get his new toy when he goes potty, it worked!!!
If he can hold his poop and pee, he is on his way to being potty trained whether he wants to be or not. (My son is 3 1/2 and he doesn't bother about "holding it," pullups are simply too convenient, and he has no role models of his own age or just a little older, to see using the toilet all the time.) If you can, be sure the boy sees the other kids lining up to use the toilet and in fact using it in a matter-of-fact way, it is possible that all the stress on the issue is making it seem impossible to him.