My guess is that there is a real magic school, but since magic is still denigrated in western culture, it is probably done quite secretly, and hidden from human view and minds. However, going forward, life has a habit of imitating fiction, depicted imagination and film (look how episodes of The Simpsons have seemingly ‘predicted’ events and circumstances) so in years to come, such a place could well manifest in reality.
Many moons ago, I saw a bumper sticker which said "Even the word Impossible contains the words "I'm possible"". I am always reminded of that when I see the word impossible (and tend to think of the words "I'm possible" in response).
I would say that Hogwarts may already exist somewhere, but also that a school like Hogwarts isn't the only means of learnign and using magic. I think there is real magic in everyday life, but often we are not open to seeing it as such.