Yes, students should review all of the learning materials in a lesson, even if they think they already know the topic. If they don't do well on a quiz, they should go back and watch the videos and read the reading links again. The idea is for students to practice re-taking the quiz until they feel they have mastered the concepts in the lesson.  Students should also use the quizzes as practice for the unit test.  The system always keeps the highest score for a quiz.