A great website you might want to check out is
www.combatgrappler.com I was fortunate enough to meet Zach Even-Esh at the IYCA conference and he specializes in training wrestlers and fighters. Zach utilizes a lot of "hardcore" training techniques. When I say hardcore I don't mean he's blasting metallica working them into the ground until they vomit (probably like your son's wrestling coach). Zach uses kettlebells, log carries/cleans, sled pulls, sandbags, etc., to build strength and power.
Zach would be a better resource than myself to talk about developing a young wrestler. Beyond being just a great coach, Zach is a great guy so I'm sure he'd be willing to throw some information your way.