As someone who mildly stutters now, the best advice to give is to get rid of the idea that you want him to “quit stuttering” because it will always be there. I used to stutter severely when I was younger, and i combatted thst by going out of my comfort zone and becoming more social by putting myself in situations where i’m forced to talk to people. Eventually it became easier. Now I still do stutter but it’s very mild . That’s not to say it will work for your son but if anything it’ll get him more confident in his speech and remove the fear of speaking like a lot of people have when they stutter