He is 100% not make a high-major D1 if he doesn't leave Bristol Central. It will be a complete and utter shame if he doesn't.
Honestly, if you know the family well enough, you should he in their ear about a prep. I usually mention to parents that the education is way better. Forget about the basketball. If you get an opportunity to get a diploma for free from a private school, you take it. That's a what, 50k education per year at some places?
ANY decent high school coach is telling this kid to get into a better school. If his coach isn't he's a selfish twerp. I have encouraged kids to move on from my AAU team, to focus on other sports, or go to another high school when it is in their best interest. If you care about the kids, you do what's best for them first and the team second every time.