I'd suggest trying rap. Let him do karaoke rap. But of course there is a lot of garbage lyrics out there. Should choose wisely. Also, I'd suggest nootropics, but that's a topic that requires some further eduction on the matter. Also, of course the diet is important, but that goes without saying. Tofu for example, but with some delish sauce, otherwise it's not very appealing. Broccoli. Most importantly a therapy, even if you read together with him, that might help a lot!! I never had the luxury of speech therapy, but I wish I had. My mom once read with me, and it really helped my. I'd just read along with her. That was one of the very few times. I was good at covering it up, so they probably thought it would pass.. Best regards!