Potty Training at age 7?

Really? I thought by this age he'd really know that pooping in your pants really is a smelly idea. Every weekend it seems he does it at least once. I don't know what's gotten into him. I warned him the last time that I would start punishing him for the behavior and talked about how embarrassed he'd be if his friends found out he pooped his pants. I was laying in bed with him doing nothing in particular when I smelled that tale tale smell. Ugh! Sent him in to get cleaned up and sent him to his room to clean it. He has spent the day in there because he decided to talk back on top of it. He told me to apologize for yelling at him for pooping his pants. Ha apologize to him for punishing him for doing something wrong? So after he'd been in his room for a very long time I finally had him come talk to me. I explained to him that I will not tolerate the behavior and if it happens again it means he needs diapers and I will make him wear them to school. I really hope that this is the last time this smelly incident occurs. I don't want to potty train a second time.