Francis7,
I like the article you referenced about Justin Turner.
You've been around the diamond enough (not calling you old at all!) for me to realize that whatever I put in this message, you're probably well aware of.
I would suggest the following book for almost any player who's twelve and older:
Play Big by Tom Hanson
If approach needs some work, I think Steve Springer is a great resource.
For some drills, I like the information that Trent Mongero provides.
Obviously, there are tons of online resources - not all of them are good - but there may be a nugget or two that your son latches onto that may be of some benefit.