A friend of mine who worked in Harvard admissions mentioned to me once that Harvard was not necessarily looking for the smartest students, they were looking for the students who would be the most successful. Outside of academia, success depends on many qualities in addition to sheer intellect and dedication (even for Bill Gates, it is not genius alone that accounts for his success). Within academia, while those qualities are more important than they are outside (on the whole, though with exceptions), there are still other qualities that influence success. And Harvard is not necessarily interested in producing a large number of the next generation of academics, at least with its undergrad admits. For one thing, Harvard can’t maintain its endowment on donations from academics.
Harvard says that it wants to admit 200-300 of the most promising future scholars in each class. Actually, from what I have seen locally, they don’t do too badly at that. But it’s a small fraction of the whole set of admits.
In my experience, it is rare that a student is counting on a perfect ACT or SAT score alone to gain entry to a top school. Students may underestimate how many students (including themselves) have the “whole package” of high standardized test scores, excellent GPA both weighted and unweighted, rigor in the high school courses, perhaps multiple post-AP courses, and very strong, but not unique extracurricular activities. Students in this category are still rejected from top schools.
I suspect that the admissions committee members at top schools become a bit tired of these students. They are looking for someone who is especially interesting, unique, or funny. They are looking for a student who tugs at their heartstrings. I know that admissions is not a Queen for a Day competition, but I suspect that an essay that somehow makes an emotional connection with an admissions committee member is more effective than you might think, more often than you might guess. Is that applicant a better person, or savvier than other applicants? In reality, most likely not. Also, the admissions committee members are sometimes looking for a student who advances their personal agenda in some way. You can see evidence of this on CC if you read a lot of it and read it carefully.
Yes, occasionally an applicant makes a real blunder–applies to Princeton and writes that he wants to continue to medical school at Princeton, or applies to MIT and writes anything that comes across as arrogant–but I suspect that is probably fairly rare among the really excellent applicants.
I think that some admissions committee members are unable to distinguish the truly exceptional high flyers from the run-of-the-mill excellent students (Harvard’s statements notwithstanding). I think some of the schools don’t care about trying to do that. Caltech probably does. But the missions of most of the top schools are fulfilled by having an adequately sized class of adequately strong undergraduates. The top colleges make their reputations with their faculty; to a lesser extent with their post-docs; to a lesser extent than that, with their graduate students; and almost negligibly, with their undergraduates.
I also think that in most cases, the students themselves have no way of knowing at the high school senior level whether they are among the truly exceptional high flyers, or whether they are among the run-of-the-mill excellent students. Nothing wrong with being run-of-the-mill excellent–it is a quality that the nation sorely needs; but it’s not the same as being extraordinary.
(If you object to the phrase “I think that . . . ,” please replace it by "It is my considered opinion, based on information I have and instances I have known, that . . . ")