OP again; thanks so much to all the PPs for such outstanding and helpful advice. You've all been so generous with your suggestions and it's much appreciated!

From what I've seen, schools that only accept one letter of recommendation tend to be larger public schools where grades and scores (rather than ECs) determine admissions. (Athletic recruits are the exception to this rule).

OP, what year is your DS? If he's a rising junior (or younger), depending on his interests, it might make sense for him to consider entering competitions like National History Day or Scholastic Arts & Writing awards, or USAMO or Siemens. These are opportunities for external validation based on individual performance. No BS clubbiness, but a chance to go beyond the classroom, and (often) to define your own project, work with a mentor, etc.

Anonymous wrote:

Anonymous wrote:Recs and essays.

+1

Recs or Rec? Some schools only accept one.

increase their odds of admission (especially at places like Chicago) if they can craft the kind of essays I've described.