First, if your son's health and injury status is important to you, you have to understand that there are about 10 coaches in the public schools of the United States of America who actually know what they're doing in the weight room. His odds are not good. Here's some reading for you:
Can You Put Your Kids on a Strength Training Program? | Mark Rippetoe
Why Your Kids Should Be Lifting Weights | Mark Rippetoe