bbman:
You can TTFWIW. Don't hold too much weight on the information/recommendations from a bueliten board on pitching - some people may know what they are talking about and many do not. Find a good pitching coach in your area and work with him to make sure you are not overstressing your boys arm. Do it now as the stresses on the arm go up significantly as pitchers start throwing over 80. Sliders are really hard on young arms...see PG's post in the general thread to the starting over kid. I won't bore you with the details but is is a Vel. Squared function.
Based on my experience you may have to go to several until you find someone you and your son is comfortable with. Actually seeing more than one helps balance the information you are getting and different coaches sometimes catch different flaws.
Also make sure he has a good throwing program and he is doing the proper things as far arm strength development, warm up, and cool down and post pitching conditioning. I happen to like Jaeger but there are others out there.
Good luck as it sounds like your HS coaches have a good handle on managing the work load part.