With young athletes who exhibit poor technical quality on a particular exercise or group of exercises, the best method of offering correction is often to become less dogmatic or predictable in your teaching method.
When teaching the squat for example, most Trainers and Coaches tend to take a ‘top down’ approach to skill execution.
They teach the young athlete to set there feet and proceed through an eccentric-concentric progression.
The nuances as to why a squat may be faulty are many, but very often, it is the inability of the young athlete to get to and summarily regulate the base of the squat phase (the ‘hole’).
When inaccurate applications of force production/absorption are applied to the eccentric and ‘pause’ phase of the eccentric base (no matter how quick or seemingly inconsequential), the ability of the athlete to apply correct force sequences towards the concentric motion will be compromised.