My son turned 4 this past summer, and we were still having issues with that also. It was clear that he was ABLE to use the toilet--he just couldn't be bothered to stop what he was doing, and also he got frustrated that it didn't come out immediately like pee does. ONe thing that helped him turn the corner, is I went to Toys R Us and bought a cool Star Wars toy (he and his dad like to watch the original movies together sometimes), and gave it to him after we caught him in the act of pooping in his pants, and he did it on the potty instead. After much praise, I gave him the toy and made it clear that this is a toy for big kids who poop on the potty. A couple of days later, he did it in his pants again, and I reminded him that his special toy was only for big kids, and put it up on top of the fridge where he could see it , to remember, but not get it down. Wow-did he have a tantrum! But he got the point. That's not to say that he has been 100% on the potty since then, but it has really been effective as motivation. Good luck.