Pitchers have three weapons at their disposal: speed, location and movement (spin). At the 14U level, pitchers will work most on speed (and how to vary it) as well as location (and how to vary it).
Using a few different pitching grips will help a pitcher develop the ability to throw pitches at different speeds accurately.
CLICK HERE to view some grips--paying particular attention to the 2 and 4 seam fast ball grips as well as a couple of the change-up grips (circle and three finger grips).