Just a note to suggest that the Preview functionality ought to be extended to be more accurate. Despite unchecking "Let students see their answers", when you preview a Classic Quiz, it appears as if someone who has taken the quiz can still see their own answers (and, to boot, which ones were incorrect) (and thus which ones were correct). Wasted a couple of hours trying to solve this before only realising it was misrepresentative when I actually published a dummy quiz and went into Student View.