Somewhat off the topic at hand, but I've been thinking about the Grainger family.

To my understanding, the wizarding world goes to GREAT lengths to keep Muggles from realizing they exist. Yet Hermione seems to have studied about Hogwarts for a long time before she got her letter. How would she know about it? And how would it be explained to her parents? "Sir and Ma'am, we'd like to take your daughter away to a secret boarding school that you can't visit, and we can't tell you what happens there"?

any ideas?