if he does strides 2-4 times a week and stays injury free I don't see why he won't make a huge improvement.
He should do just mileage and strides. If he does workouts he'll get injured for sure. And I'd recommend he does a few summer races just to break up the monotony and to instill confidence that it's working.
Also, its important that he sticks with it. He'll feel like a zombie but needs to stick with it. You can't just do high mileage for a month and declare whether or not it works. It takes years of hard work to fully realize all the benefits of it.
My prediction if he actually does it, stays injury, and does strides 2-4x wk: 1650-1720. 2016 though he'll really notice the benefits and probably run like 1610-1620.
Just my 2 cents. He's just jv, so encourage him to do it. If he improves a lot and makes varsity, then your team is better. If not, well he's jv so it doesn't change anything.