I have two boys playing college baseball now. One (SS/RHP) throws 90s in his sleep. The other (SS/2B) needed a lot of work to improve.
Driveline is a great program. My boys also did the Texas Baseball Ranch and one spent time at the Florida Baseball Ranch. Echoing the Rover, Wolforth is great. I'd say Randy Sullivan in Florida is much more approachable (and a physical therapist). The Elite Pitcher's Bootcamp is a nice weekend introduction to the Ranch's concepts. Whether it's one of the Ranches or Driveline, their ideas have been tested.
IMHO, a lot depends on what the kid is able to do once they're not at a training site. A lot of coaches won't or don't subscribe to Driveline's or the TX/FL/AZ Ranch concepts and it makes training alone or at your home location pretty challenging.
You mentioned your son hitting the weight room for the first time this Fall. I can't emphasize that enough, if done correctly. He's got a lot of time at this stage to really build himself up. My older guy trained at Cressey in Massachusetts; my younger guy at Sparta in California. These were very focused training/conditioning programs optimized for the athlete (age, sport, etc.). Conditioning done right will help build a player's body...and as a result in my sons' cases, help them throw harder.
Hopefully he can find a great conditioning program, and a great velocity improvement program. As with a lot of things, it's time and money. But for a pitcher, particularly a young man like yours, it can be $ well spent. Good luck!