In the winter (in our garage), I used to flick tennis ball can lids to my kids as a way to practice batting hand eye coordination on curve balls. Two of my sons got frustrated every time and found something better to do. My oldest stuck to it (extremely motivated to not be a PO on his travel team), and became pretty good at hitting curve balls when he got to high school.
To Goosegg and NYCDad's point this is about motivation and drive at a young age. Dominicans have it in abundance when it comes to baseball.