I am talking about motivating him to do that little bit of extra work outside of official team activities.
Work with him on finding a mentor (or two or three). It can be someone a year or two older, a coach, or someone going to college playing multiple sports. Someone he (and hopefully) you can contact in the tough times. My son has a couple. Kids who have graduated high school, took many AP and honors courses, and playing and doing well at the next level. I can only cajole so much. Sometimes I suggest to my son that he contact one of his mentors, or I'll contact one of my son's mentors and ask if they wouldn't mind contacting him (just to say hi, leaving me out of it). Video also works. Just show film of a bad at bat, poor pitch, missed tackle, bad three point shot, etc. Makes the point and you don't have to say anything. Of course, if your son is a lineman in football you can always use food. A real lineman will do anything for food.