@ghostotter: I want to assure you that the level of care and instruction at Mercersburg Academy in Pennsylvania and at The Culver Academies in Indiana is outstanding.
Schools like Andover, Exeter, St. Paul’s, Groton and a couple of others are for students who are off the charts brilliant and need much more challenging instruction than offered in typical high schools across America. (Talented athletes can be an exception, but are often asked to repeat a grade upon entering an academically elite boarding prep school.)