Welcome to the Fellowship of the Bump!
I’m something of an anomaly on this website—I had learned the basics on my own, and as a result of my curiosity about the slider I found a most incredible pitching coach. My training was strictly major league as a result. My pitching coach of long ago—an active major-league pitcher—firmly believed that each pitcher has a natural motion, and what he would do was work with that pitcher to help him (or, in my case, her) make the most of it, take full advantage of it.
As a high-school pitching coach you might want to be aware of this; you’ll have an assortment of different pitchers of different abilities, and so you might think in terms of individualization, of working with each pitcher to help him maximize his capabilities. 8)