First thing to do is have an honest assessment of where your son is from a quantifiable skills perspective, and an academic perspective. There are a lot of great schools out there, so just being honest about those two huge items helps to narrow it down. Then get a sense of other large factors. Does your son mind being far away, or does he want to limit travel to a 3-4 hour car ride. Weather a factor? Size a factor? Caught up on D1, or open to all Divisions? Winnow all of this stuff and then you'll get to the ball park of 30-50 schools to really start evaluating.