At Andover, the average SAT score is 1400 and the average ACT is 30. When you look at their matriculation lists, they have admissions success far beyond what you would expect just by looking at the stats. A very large part, probably most, of that is Andover students have numerous hooks. However, I would bet Andover itself adds to that(whether by having GCs/teachers who know how to write great LORs, teaching students to write in a way appropriate for essays, variety of ECs available, or being respected for the rigor of their curriculum.). I’m theorizing the admissions advantage depends on the student and the college applied to. If your goal is Harvard, there’s probably a long line of hooked students ahead of you at Andover. If you’re trying to get into somewhere other than HYPMS, it probably helps. How the college admissions process works is a separate question from how any of us think it should work.