I've been working with a local middle school to help them implement Moodle. The math teachers have started using it and I helped them do a quiz. They typically allow the students to fix the errors in the quiz on a second attempt for half credit. It looked to me (never having built a quiz that did something like that before) as though Each Attempt Builds on the Last would be the way to fix that. I'd expect, though, that each attempt builds on the last would do something about removing questions that were already correct or at least showing that some of the questions already had correct answers. Neither of these seems to be the case so I can't see what good enabling that setting does. The documentation isn't very explicit (a use case would be helpful) and setting some quizzes up on a sandbox server to see the behavior hasn't shown me anything. So, I guess two questions.
a) Is there a way to have students take a quiz to correct previously wrong answers without having to write down every answer they previously had and effectively re-take the entire quiz again?
b) How does Each Attempt Builds on the Last actually work and what is the use case it was designed to fulfill?