This year many top schools witnessed acceptance rates far below the twenty percent benchmark (Andover had 16.6% for reference). While the "Big Three" colleges may prove to be an exception, the Ivies seem to have an acceptance rate revolving somewhere around 15%.
Somethings to note:
Boarding schools have a far more self selected application class
Fewer people apply in the whole scheme of things
Every idiot applies to Harvard, not everyone applies to boarding school
While (HADES GCM) may be famous, they are not Harvard famous
Taking this and more things into consideration why do these schools have acceptance rates that parallel Ivy and top schools?