Here's what I have noticed with colleges in the Northeast.
The roster of most of the colleges that I've seen in the Northeast are made up of players that are garnished within a 90 mile radius. There are a few players from beyond that distance, but they are not the representation of the player's pool. College coaches tend to rely on a known source that has demonstrated itself to be reliable, easily accessible, an alumni base that has good networking, boaster club support and so forth. The reasons for this mindset by college coaches are because of their lack of resources, both in time and money to find talent.
Parochial colleges tend to use parochial schools as their source of players - but not always. Private colleges have an alumni base that are more than willing to support ANY athletic program, sometimes with deep pockets, and that means funding for a variety of things. These persuasions can do more than just attract attention from a coaching staff.
You would get a much better picture of any college or university and their club's makeup, what their coaching staff looks for, and where they get their player's pool, by reviewing their roster makeup. Do most of their players come from the same school? Are they mostly from the same part of the state? Are pitcher similar in any way?
Here's something to consider when receiving mail from camps and such from a college or university that's out of state. Lets say that you live in New Hampshire and you receive a letter of interest from ...oh ... the University of Miami. Your invitation is the fly down, tryout, and meet the coaching staff. Now with a bumper crop of ball players in Florida, the makeup of that clubs roster will tell you a lot of your son\s pecking order in the universe with respect to the University of Miami. Also, their game history will also tell you who pitches a lot, and who is use as back up... and little else.
Your son's high school coach should be on top of all this - IT'S PART OF HIS JOB, by the way. Also, these travel teams are also staffed with people that should have contacts.... quality contacts, not promises, to introduce your son and even provide letters, of recommendation.
This business of attracting and contacting college and university baseball coaches is just that ... A BUSINESS. Treated as such. Every time your son suits up he's ready for an job interview. The way he looks, his language, his presence on and off the field is being watched. By the way, if your son has promise, pro scouts may approach him - but that's for another posting.
Consider this venture as a sales team " selling" a product - the product being your son. Your entire family has to pull all the stops, talk to everyone and any they know. Ask about the colleges and universities that has the academics that your son is interested in, then go after that baseball program tooth-m-nail. Do you and your family know any alumni, can you and your family use any contacts with all the teams that your son played for, and so on. The main thing here is don't be shy about your son's interest once he makes up his mind. Coaches like aggressiveness - not a pest. Provide them with a real product that they can use makes life easier for them. Be polished about this approach. Go to games, if you can, and sit right about their dugout. A glance in the stands can jog the memory of a coach when it comes time to make contacts by a little ... " hey, I've seen this kid before... now let me think.." If that college or university of interest has a time and place for pitcher tryouts, take advantage of it. These things are an excellent time for your son to look at his competition.
Best wishes with you baseball experience.
The NCAA has a division system that ranks colleges and universities by size and many other factors.