Theoretically, there are advantages to working with students of the same ability and different ability (Lou et al., 1996). In order to determine how students ability affects the peer-review process, students writing ability (e.g., high-ability versus low-ability) was first determined. Then students were randomly assigned to review either four high-ability peers papers or four low-ability peers papers. In return, they received feedback from either four high-ability peers or four low-ability peers. The quality of students second draft of their first paper and the quality of the first draft of a second paper were analyzed to determine whether students learning was affected by the feedback they provided to high-ability versus low-ability students and by the feedback they received from high-ability versus low-ability students. In addition, several mediators (e.g., motivation, amount and type of feedback) were examined to explain the learning differences.