Calibrated Peer Review (CPR) is a program, for networked computers, that enables frequent writing assignments without any increase in instructor work. In fact, CPR can reduce the time an instructor now spends reading and assessing student writing. CPR offers instructors the choice of creating their own writing assignments or using the rapidly expanding assignment library. If you believe in constructivist learning, writing is the most important tool that you have. But if you have a class of 300 students, grading essays challenges even the true believer. Calibrated Peer Review (CPR)can be used in classes of any size. CPR is based on the model of peer review in science. The student reads a document, either on-line or hard copy, then writes about it. When the student has demonstrated competence as a reviewer, the program delivers three peer documents on for review. The student answers content and style questions and assigns scores. Finally, the student does a self-review. The student grade comes from writing and reviewing. Even though the program is only in its third year, approximately 100,000 students have used it. Although CPR was designed for use in large chemistry classes, experience has shown that it can serve in many other disciplines, as well. Currently, business, chemistry, economics, English, and life science instructors are using CPR in college, graduate and professional, high schools and middle schools. CPR was developed in the Chemistry Department at U.C.L.A. with funding provided by the National Science Foundation and Howard Hughes Medical Institute.