college or minor leagues

Sounds like the scout questions were probing to find out about your son's "sighnability".

If your son (and/or the parents) make the scout feel that moving on to D1 is a high priority, then his  "sighnability" tends to go way down resulting in being push to the much later rounds.  If son's interest in going pro is an overriding factor, the "signability" goes up.    

It's difficult to juggle without shooting one's self in the foot one way or the other. 

Is it word of mouth that the other teams find out about his intentions resulting in the slide down the draft board?

Some word of mouth gets around between scouts and recruiters, but mostly it comes from the types of answers given to the scout's questions and answers on questionnaires that are filled out.  As a parent, you've got to be careful what you say in the company of a scout or recruiter too.  And the scouts DO try to read between the lines to try and see which way the player is really leaning. 

I know there is at least one great thread discussing the pros and cons of going pro out of high school - probably 3-4 months old.  I don't see this scenario much different than the high school discussion.  Several folks argued quite strongly that an education is far more important and should be pursued unless offered "life changing"money.  If you see a path to move to a D1 and finish with a degree, then by all means that should be pursued.  Similar to high school grades, a scout will make an judgement as to whether a kid can actually move from JUCO to D1 from an academic standpoint.  If grades do not allow for this move, then the scout will know that the kid has little leverage.  Based on what I have read here, I would suggest that he work hard in school and on the field - and work towards securing a D1 spot.  He will be eligible for the draft this June regardless and possibly the following June (after second year at JUCO - assume he is a freshman).  The more options he had, the more leverage he will have if/when he does get picked.  Signing money in the lower rounds ranges between ZERO and $1,000,000 - just depends on talent and what it would take to overshadow his other options.