Refusing to enroll in Hogwarts
Imagine a Muggle-born. Muggle-borns have absolutely no idea that magic exists, and I remember seeing an old thread from last year (or even older) where the general consensus was that a Hogwarts teacher would deliver the letter personally to the Muggle-born and explain everything.
However, what do you think happens when someone refuses to attend Hogwarts? I mean, the Muggle-born sends an owl back to Hogwarts saying that they don't want to attend Hogwarts, but do you think they even get an answer? Do they get a second visit in order to be convinced ... ?
What do you think?