S.T. Ockenner
Istar
I'd say its the other way around. Fantasy with a boarding school as a background. After all, the magical elements are way more important to the plot then the boarding school is.I don't know about the Earthsea thing (only because I never read that series) but I read a lot of Enid Blyton as a kid. I would agree with you about Harry Potter being nothing more than a British boarding school story with fantasy elements tossed in.