Jason - although a relative newcomer myself, I think the problem lies with the parameter "Retakes allowed" which you have set to "No". If you set this to "Yes", the student will be able to take the lesson many times, and Moodle will record the mean of the scores as their grade.
Now - I'm not sure that what you really want is to allow the student to fully retake the lesson (e.g. answer each question again). But I haven't found a way for a student to simply review the content while skipping over the questions - it seems every question page absolutely requires a response in order to proceed. If you find a solution to that problem, I'd love to hear it.
Stan