As a graduate of both an American school and two British universities of very high standing, and someone who has done a great deal of research and visiting of private schools around the nation, I can say without a shadow of a doubt Germantown Friends stands head and shoulders above almost every other school.
I knew very little about it (but had heard of it) ten years ago when I chanced to discover that a fellow student of mine at Oxford - a singularly brilliant person - had gone to GFS. At the time, I was doing research into educational environments in the US and the UK and was due to return to the US for an extended period of work. So I put it on my list. After at least eight years of looking at schools across the nation, and interviewing hundreds of students, former students and parents of many, many excellent public and private schools, it would be pretty difficult to come away without GFS being one of the top schools on the list, along with Sidwell Friends in Washington DC., and several others. It is a school that manages to balance a very serious and rigorous focus on deep knowledge of the fundamentals (at a very high level) with an unpretentious, solid backing in values that are truly carried forth beyond the school into students' lives.
Beyond these broader assessments, from just a nitty gritty college prep perspective, I think one quote from a former student I interviewed was an interesting assessment. He said, "I didn't truly appreciate my education at GFS until I got to my sophomore year at Cornell, and realized we were reading books that I had read in eleventh grade."
All I can say is, I wish I lived in Philadelphia so that I could send my daughter there.