Back to your question. I provided a link to Steve Ellis site with various grips of pitches for reference…..thanks Steve.
http://www.thecompletepitcher.com/articles.htm
The slider is the most damaging pitch there is for young arms (other than over use), many throw them with no problems however; it is just a risk issue. I personally don’t let my son throw them nor would I recommend them to anyone else. Most pitching coaches suggest you wait until college to throw them. As someone mentioned earlier in the thread you can pitch effectively with a good FB, CU and CB in High School. Heck you can pitch effectively in HS with two good pitches. The better your FB, the better chance you have moving up to the next level. It is that simple.
As Steve mentions in his site the differentiation between a curve, slider, cutter, slurve is based on the axis of spin and somewhat subjective. A slider will spin like a football with the “red dot” (axis of spin) toward the batter. That axis shifts around depending on how a ball is thrown and it is subjective as far as when a slider becomes a slurve, or a curve or a whatever.
Every time this issue comes up I repeat what most good pitching coaches will recommend.
Pre-HS: Focus on FB and CU
Freshmen HS: Learn how to throw a proper curve. It usually takes about a year to develop a good high velocity hard breaking curve as opposed to a loopy slow one. Continue to be obsessed with velocity and mechanics.
College: Learn a slider...maybe.