I went to a Quaker school that is considered an elite prep school, but I certainly didn’t consider it like that as a young student. It was just a healthy learning environment and a caring community in which I thrived… subsequently my kid went to a Quaker school for the same reason, … Dewey kid is now at Putney, a progressive boarding school in Southern Vermont. While there is no Meeting for Worship, in my opinion it is entirely similar in principles and pedagogy. It’s a simpler campus than most of the schools you described, but that is part of it’s truly progressive mission as inspired by John Dewey. Have a look.