I'm thinking of a few apps you could share with him and maybe do together. One is delayed auditory feedback (DAF) apps. You speak with the headphones in and the delay helps (some) with fluency. You could try it too, increase or decrease the delay and play around with it. Try some guided meditation apps/ videos with him. Do it together and see if it helps with his fluency. May give him tools to use when he's at school, etc. YouTube diaphragmatic breathing techniques and do them together. Practice A LOT and remind each other throughout the day to breath. This has helped me tremendously. Start with the TED talk on diaphragmatic breathing... very cool stuff. I hope these are some useful tools you can give him and experience together. Worst case scenario they don't work for the stutter at all, but at least you got to spend some time together and the meditation and breathing can help overall health anyway. PS... sounds like you're doing a great job and he's lucky to have you as a parent.