Sidearm pitching

Question
My 15 year old son, 6'2" 190#, LH pitcher has fallen in love with a 3/4 to sidearm delivery.  He has great control, and a breaking ball that seems to start behind LH batters, and has them bailing out every time.  His fast ball has a natural break to it, about 70-75 mph.

He is attending a baseball academy, and the coaches are in love with his pitching, and do not want to change a thing.  They agree that he is a Division 1 prospect, and "could make millions as a specialized receiver".  

Your thoughts on developing as a sidearm pitcher, and any particular drills or skills that he should concentrate on.  I had been working with him to "come over the top" more, but after his coaches reaction, he is reluctant to change.  

Answer
The tough part of this situation is that your son must first get into professional baseball to start 'making millions'. While i do think he will get Div. 1 interest because he is left handed, and tall. He will have to develop arm strength to pursue a pro career.
All the Lefthanded specialist making millions today, threw a lot harder in their prime. They are often converted to throwing sidearm to prolong their career.
that said try and get him to focus on the following aspects of his game:
1. Learn to throw at a 3/4 arm slot. there is no need to go higher or lower to be any more effective.
2. Learn to command a Two-Seam fastball down in the zone, to both sides of the plate. (it can be a four-seam, if there is natural movement)
3. Develop a breaking ball to get out lefthanded hitters. It should look like the fastball out of the hand and only needs a little break. Be sure it has depth (breaks down) and doesn't 'sweep'(breaks left to right on the same plane) across the plate.
4. A change-up is a plus for getting out good righthanded hitters.
5. Long toss to build arm strength. To be seriously considered as a professional prospect his velocity will need to be at or around 90mph. He is still very young so don't worry to much over this. I only threw 86 as a senior in high school. it wasn't until I was a sophomore in college that i started throwing in the low 90's. Thats where going to college can help him.
Overall i think that he has plently of time to develop, but don't let him limit himself to a 'left-specialist', lefthanded starters make way more!