@Wisdom2share Of course there are no guarantees, per se. And there are nuances. As well as overarching trends. For example, on average Harvard takes as many kids from Exeter as it takes from the entire Rocky Mountain region of the United States! (Colo, Utah, Idaho, Wyoming, Montana.) 
It just so happens that those Exeter kids may be also legacies, or children of VIP parents and they happen to be at the right school and aiming for the right universities.