How do you hit the curveball?
How do you hit anything other than a fastball down the middle?
Adjustability the answer those common, and critically important, questions.
Adjustability is exactly what its name implies; the ability to adjust to the type, movement, and location of the pitch.
If you are going to be successful beyond 6th grade or so, you have to learn about the three main types of Adjustability...
I have put together a number of pieces about Adjustability...
... X-Axis Adjustability
...... X-Axis Adjustability and Hip Rotation
... Y-Axis Adjustability
... Z-Axis Adjustability
...... Delaying Mechanism
... Adjust Late
X-Axis Adjustability enables you to adjust horizontally and cover the inside and outside parts of the strike zone.
Y-Axis Adjustability enables you to adjust vertically and cover the top and bottom of the strike zone.
Z-Axis Adjustability enables you to adjust to the speed of the pitch and hit off-speed pitches like change-ups and curveballs.
 I think one of the weaknesses of Mike Epstein's system is that he generally ignores the concept of Adjustability and, when he does talk about Adjustability, he gets it wrong.