Applying to college and ever asked yourself this question? Let me provide an answer:
Since the prep schools are usually extremely well financially endowed they, first of all, have a very large assortment of AP classes available to their students (more than usually offered at a public school). The more AP classes you take, the more qualified the Ivy League schools see your candidacy.
The prep schools also have teachers and guidance counselors who, more than likely, are Ivy League graduates themselves and so know what is required in terms of achievements and classes, and try to guide and mentor their students accordingly.
Prep schools also usually have MUCH smaller classes, which means the teachers really get to know their six students, for example. Think about the difference that could make when writing a recommendation letter = having SIX students you know well who are applying to college, versus 30 in a class. That’s part of the difference.
Furthermore, the schools themselves, especially if you’re talking about the elite prep boarding schools in New England, or the top private schools in NYC, have intense admissions criteria themselves, that ensure that only the top students who apply are even offered this “best-of-the-best” opportunity.
The prep schools themselves also are usually very active in extracurricular sports and activities (sometimes at the Olympic level) that bring recognition to the school nationally.
Then there’s the fact that the admissions officers at Ivy League schools have come to know that any student who went to such-and-such academy is going to be a likely candidate for the Ivy League, otherwise they never would have gotten in to their current prep school. This makes the admissions committee’s job easier, as they see a student from that school and they immediately go to the top of the pile for serious consideration.
Schools like Harvard and Princeton and Yale also maintain close relationships with guidance counselors at the top prep schools and basically recruit there.
I, myself, though got into Harvard from a public school! It is possible and a lot of my friends at Harvard went to public school, too.
Hope that helps!