Why do you fear Harry Potter so much? Look at all those teenage-dramas on t.v, all of them are set in a typical highschool, and why shouldn't they? They are studying to become something/something later in life after all right? Why should fantasy be any different? Your characters need education, and since they are in a fantasy world, they need a specific type of education, nobody is going to point at you and say "plagiarist!", if your story is set in or around a magic school, J.K doesn't hold the exclusive rights to this literary feature.