"Cannot remember the words" is likely a lie. He got frustrated and took the easy out. First thing you need to do is make sure \*your\* energy is positive. Kids are super receptive. If he detects that you are struggling with his stutter, it's going to impact him. Next is assure him you'll listen for as long as it takes. There's no rush. Don't try to help him at this point. The less interference with his speech, the better. Again, kids are smart. And you've indicated he's bright for his age. You don't want him to become self-conscious of his fluency. I'm not advising against chatterbox or any other resources. I'm just suggesting you not ad hoc solutions on your own. Finally... It's common and often resolves itself. I like to see parents look into early intervention. But I suggest taking a breath and not stressing over it (going back to my first point.)