This study investigating the effectiveness of Calibrated Peer Review (CPR )[TM] in a senior-level biochemistry class had three purposes: to (a) compare the CPR process for feedback with TA-generated feedback in improving students' ability to write scientific abstracts; (b) compare CPR results for males and females; and (c) observe whether CPR improved the quality of student writing. Statistical analyses of three assignments by 50 students indicated significant differences between CPR and TA feedback on student writing quality. In addition, while scores of students who received TA feedback decreased, scores of students who had CPR improved. Students also progressed in CPR-generated measures of their writing and reviewing abilities. A separate analysis including 256 students found no significant differences between males and females. In addition, students' writing showed statistically significant improvement in CPR-generated scores. (Contains 4 tables.)