I took the implication from reading the books that Rowling had different ideas at different times whether there were intended to be multiple schools of magic in Britain or not. It was referred to in the beginning as the "best" school in Britain, but by the end of the series, the Voldemort-run Ministry instituted mandatory Hogwarts attendance for all youth, and a character remarked that parents had at least had the option of homeschooling their children before.