One of the options available when adding a new assignment in the Assignments tool is Peer Assessment.  Enabling this option facilitates a student peer review of assignment submissions by other students in the course.  Peer review allows students to review and critique each other’s work within parameters set by the instructor.

To add this option to an assignment, please see the Peer Assessment (Optional) step in the article How do I add an assignment?  

Once enabled, Peer Assessment has three phases, the student submission phase, the peer review period and the assignment grading.