If you can, find an slp who specializes and understands stuttering. Most SLPs get either very very little training or poor training in stuttering. So be aware there's a likely chance his school SLP is not experienced in helping a kid who stutters. What does the IEP look like? Are the goals mostly around fluency? Someone already mentioned the NSA. The other organizations I would advise you to look at are the Stuttering Association for the Young (SAY) and FRIENDS. FRIENDS might be more teen oriented, but they are both phenomenal organizations that can really make a difference. I don't know how active they are during covid, but post covid I would definitely get in contact with them. Probably the best thing you can do for him is to introduce him to supportive communities like these where he can make friends, develop confidence, and find great role models.