15 year old here with a stutter that isn't as bad as what your son seems to have. My dad deals with it, I guess. 1. First thing I can say is choose when you finish his sentences. If it's practical, obvious what he's trying to say, or needs to be said quickly, then don't feel too bad finishing his phrase, but any other times, don't. 2. Investigate into finding a good therapist. The two you mentioned don't seem too great, based on a cursory reading. 3. It'll get better. As people age, we're *supposed* to get more mature, meaning more people will understand. The actual stutter might improve (meaning less stutter): I know my stutter was worse at 13 than it is now. It might not seem like it, but it does. Mainly, you find better words that you don't stutter on, sort of like how you mentioned. It's different case to case. ​ Good luck, man. And also, if your son would like somebody to chat with somewhat his age with a stutter, please let me know, I'd be happy to chat with a fellow stutterer.