DS was in crazy good shape and decided early on that he didn't need to practice throwing a basketball.... big mistake. Even though he was strong enough to max/near max several CFA events (including PushUps and PullUps), his Basketball Throw was embarrassing! I believe there is a sticky thread on the USMA forum about this event. It seems like it really is all about body mechanics/technique.
The other thing I can suggest is variations of exercises. Because of the high reps required during workouts for many of the events, the boredom factor is pretty high for teens. So help your candidate by introducing them to all of the variations available and mix them up. Eg 1 set of regular pushups, 1 set of spider man pushups, 1 set of one-leg pushups, 1 set of elevate pushups interleaved with 1 set of side situps, 1 set of flutter kicks, 1 set of twist sit ups, 1 set of pike ups, and 1 set of regular situps. You get the idea. There are probably several dozen variations of pushups alone available to keep things fresher and more interesting.
Hope this helps and good luck!