This is a great thread and the one thing I see missing (at least I missed it) was the importance of mental toughness. My son who just got home for Christmas and I were talking about his time playing and he said the major difference to the guys who performed well throughout the season were their mental toughness. He said one of his teams top pitchers had nowhere near the stuff of some others, but he was a mental giant. No matter the situation he would control himself mentally and he was always in the frame of mind that NO ONE was going to beat him. Conversely the "best pitcher" on the team was unhitable in practice but could never get it done during real games.
The top players also know how to focus on baseball when it's time to play baseball and focus on school when it is time to be doing school work. Being able to switch back and forth with intensity and focus is what really separates many top players, at least according to my son.