My son won't stop pooping his pants

I'm at my wit's end with this. I have a 5 year old son who won't stop pooping his pants. We've had trouble with him in the past with wiping his butt well, but that is understandable for a five year old. But lately he has just been straight up pooping in his pants. It happened twice today. The first time I was pretty restrained, I explained that he couldn't go to school if he did that, and no one would want to play with him if he smelled like poop. I thought I had gotten through to him, but a few hours later, he had done it again. He just does not seem to mind that he has a big smelly load in his pants and I have no idea how motivate him. I threatened to take away his big boy underwear, but I'm afraid that he will just be happy about that because he can just poop in pull ups all he wants. I don't know where to go from here, and any help would be appreciated via /r/Parenting https://ift.tt/2YjcU1h