This study examined the impact of teaching students to provide and incorporate peers' feedback on their partners' second language (L2) writing. Sixty-five participants enrolled in Spanish composition classes were assigned to one of three conditions: trained peer review (n = 21), untrained peer review (n =21), and a non-peer-review comparison group (n = 23). Each group produced narrative and expository texts that were analyzed and scored by three raters to determine the extent to which students' text quality improved from one version to the next as well as throughout the semester, and what type of feedback L2 learners incorporated into their revisions. Results showed that participation in systematic training involving discussion and interaction with their peers allowed L2 learners to provide significantly more comments that contributed to substantial gains in final text versions. By receiving feedback from a trained L2 peer and incorporating a higher number of peers' comments into their text revisions, L2 learners were able to effectively use feedback that led to better text quality.