One of the most important parts of learning is getting feedback. With feedback, students can learn why they may have gotten something wrong, and maybe even more important why they got something correct. By focusing students on reflecting on their own understanding, students are better equipped to know when they need help.
Peer-Review feedback is useful in two ways:
1. In large classes and MOOCs, providing in-depth feedback to each student is unrealistic. In order to still provide effective feedback, I build into my classes peer-review assignments. For each peer-review assignment, I write a clear rubric for completing the assignment, and a clear rubric for providing feedback on the assignment.
2. When students are asked to review other students' work, they are able to see other points of view, and are given a chance to explore the topic at a meta-level; understanding the important aspects of the assignment (via the rubric) and being able to assess other's work. This skill improves their ability to assess their own work before submitting it, and gauge the important lessons with each assignment.