Talking a lot in class is not a behavior issue. You've said the he's a smart child doing well at school. As he doesn't have any other problems and is doing well in studies, it's clear that he just is a friendly child and loves to talk.And then, you're not in the class with him, his teacher is, isn't it? So how are you expected to help? He needs to be handled carefully by the teacher. I know I am no help but please don't resort to any punishment or anything like that.