I'd suggest tracking eat habits and seeing how much calcium (or any other vitamin, mineral, etc) you (or your son) is getting. MyPyramid.gov has a tracker that you can use. It's free
I think many people would be surprised at what they actually do get! I have been doing it the last few days, and while it's not the greatest out there probably, it works.
I have gotten an average of 730.225 mg of Calcium without consuming any milk. The recommendation is about 1000 mg but I would guess it might be a little higher for athletes.