I agree with RJM. For my son's development it was about off speed pitches. His junior and especially his senior year, he could just throw his fastball by most hitters. For the better hitters, he utilized his CB and slider as well (pitching coach called pitches). He probably threw 90% fastballs. What he never developed in HS was a change up. He worked on it some but never was called in HS because coach felt that a hitter who could not catch up with his fastball, the change up might be within his ability to hit. At time made perfect sense and coach was right as far as throwing fastball by most of them.
If he ends of at less talented competition. Just be sure to work on and develop the off speed