I think there’s a growing perception in certain private boarding and day schools that if you’re high-stats and unhooked, UChicago will often give you a very good look - particularly if you apply ED or otherwise communicate directly or via your college counselor that you’ll matriculate if admitted. It suits UChicago: average scores, yield and the proportion of full payers all go up.
Some examples of New York high-end private day schools to go with the others cited by @85bears46: at Trinity, UChicago ranks seventh in matriculants over the past five years, trailing only Harvard, Penn, Cornell, Brown, Columbia and Yale: https://www.trinityschoolnyc.org/page/Our-Program/College-Counseling/Trinity-School-Matriculation . At Brearley, it’s fifth after Harvard, Columbia, Princeton and Brown: https://www.brearley.org/page/academic–student-life/upper-school/college-advising . At Collegiate, it ranks equal-ninth in this period: https://www.collegiateschool.org/page/academics/college-guidance . At Dalton, it’s 16th: https://www.dalton.org/page/programs/high-school/college-counseling. Equal-fifth at Chapin: http://www.chapin.edu/page.cfm?p=3725 .
I’d be surprised if these numbers don’t continue to rise - both because of UChicago’s recent climb in the rankings and because UChicago is clearly communicating that these kinds of kids are a priority.