In the Spring of 2011, two of the authors of this paper taught number theory courses at their respective institutions. Twice during the semester, students in each class submitted proofs of two to three theorems to be peer reviewed by students in the other class. Each student wrote anonymous and formal referee reports of the submitted theorems, which were then returned to the original student author. In this paper we detail the peer review process, discuss a survey that gauged student perception of peer review, and reflect on the strengths and weaknesses of this pedagogical method.