One approach to writing instruction that has been shown to improve secondary students' academic writing without increasing demands on teachers' time is peer review. However, many teachers and students worry that students' feedback and assessment of their peers' writing is less accurate than teachers'. This study investigated whether Advanced Placement (AP) English students from diverse high school contexts can accurately assess their peers' writing if given a clear rubric. The authors first explain the construction of the rubric, a student-friendly version of the College Board's scoring guide. They then examine the reliability and validity of the students' assessments by comparing them with their teachers' and trained AP scorers' assessments. The study found that students' assessments were more valid than the ones provided by a single teacher and just as valid as the ones provided by expert AP scorers. Students' and teachers' perceptions of the peer review process are also discussed.