First, his diet looks good for an active 14 year old. The "eating all the time" is good, as having several meals as opposed to just 3 is much better for not only his metabolism, but also for his bristling testosterone levels, which you'll want to keep as elevated as naturally possible.
As for protein supplementation. I really hate to suggest any whey, casein or egg products with an already elevated cholesterol count. If you insist on going that route, the only "new" thing is one of the more obvious ones. Some companies have discovered that mixing both slow and fast burning proteins are the best way to go, as opposed to just making a product with a big number next to the "grams of protein per serving" on the jug. Google "Syntha 6" for a good explanation, and you can probably find some product reviews as well. Were it up to me, I'd suggest a soy protein. For starters, soy has a better bioavailability than most of the whey crap that's out there. Studies have also been done on soy v. whey in the antioxidant department, and soy appears to be easily winning that one. I personally use and like NOW Soy Protein. 2 lbs is around $10, too. You'll probably get a better price online than you would at GNC (who likely doesn't carry it). A health food store might very well have it. Since he's looking to add strength and not just pack on muscle, he shouldn't need but maybe one serving of it per day. Oh, btw, it tastes like crap. Something to keep in mind.
Okay, now here's the bump. Because of his activity levels and the amount of "weight" he's moving, I think it's worth thinking about supplements beyond protein. Naturally, have a talk with his doc first, but I think he'd benefit a great deal for a high-quality creatine and nitric oxide mix. Going this route, plan to spend around $50/mo. It's not cheap, but the effects should be fairly dramatic. I've mentioned this before over in the fitness forum, and I've personally been using it for a couple years with good results. BSN makes a product called NO-Xplode. It's a creatine/akg powder. Rather than going into potentially rule-breaking details about how it works/what it does, I'll let bodybuilding.com do it for me:
http://www.bodybuilding.com/store/bsn/xplode.htmlI stack it with Cell Mass (also from BSN), but he probably doesn't need the recovery aspect. It might benefit him to take a small glutamine supplement post class/workout. I also take it differently than the directions suggest. I take a full serving of the NO 40 minutes before I hit the gym, but I also put a serving of both in my water bottle to drink during my workout.
If you go to GNC looking for creatine, do some research first (or ask me, why not?). They may try to sell you some monohydrate or some other crap from the 80's. You want the quality stuff.
Lastly, though I have no idea where he'd find the time, consider having him join a gym. I joined my first gym when I was around 13 or so, and bought my first weight set when I was 14. The best way to get stronger is to progressively lift more weight. Now, unless he's going to start lifting heavier girls every couple months, he's not going to get much stronger.
I'm sure I missed something here. I'll reread this in a couple hours and add to it if need be.