Online practice quizzes can be used to supplement instruction in the classroom. Such quizzes can engage retrieval practice, thereby improving learning and retention. However, despite their potential benefits, recent work suggests that students typically underutilize online practice quizzes. This article reports an observational classroom study, in which students were provided optional online reviews throughout the semester. The reviews could be accessed in test format, in which students were given multiple-choice questions and provided correct answer feedback, or in read format in which students were given the same questions and were shown the correct answers. Students who used the test format performed better on exams than students who used the read format or did not use the reviews. Nevertheless, the massive majority of the online reviews (approximately 88%) were not completed, highlighting the tendency for students to underutilize optional online reviews.