Rob,
Good topic.
About 10-11 years ago when everyone of my son's teammates were having pitching and hitting lessons we were told not to do anything with him.Let his natural ability and instincts, desires work, don't try to change anything. We followed that advice. But that doesn't mean it would be the best advice for others.
I have seen so many players take lessons after lessons to improve, play on the best teams, go to the fanciest camps, and never reach what some many think is their potential. Is this because there comes a point where whatever you do will not make him a better player?
I have also seen many players grow up and reach their potential after the HS experience, with good coaching in college or in pro ball. Many players who never seemed to be even a pro potential become a first rounder, surprising many that they never thought he was "that good".
I have see too many parents push their players to be more than they might ever be, sometimes it works out well other times it doesn't. Most young players have no idea what it is to "reach the next level". Parents that put their own desires aside for what their children really want usually find that their children grow up and become smart and will move to that next level successfully, if they want to. Yes, kids do change, and those that are pushed to their limit too often lose the desire and those that are allowed to play and have fun surprisingly move ahead. As PG states, some move ahead on natural ability, some on hidden ability (physical and mental maturation) and some on developed ability.
I have to agree with CD, you can't make generalizations because all players are different and all players progress and grasp things differentely. And all players have different desires mature differently.
And I agree with infielddad, how the game is played after HS forces players to make adjustments that will move them ahead or not move them ahead.
There was a topic about not where you begin but where you end up.