The value of proctor written feedback on college students' graded quizzes in a Personalized System of Instruction (PSI) was investigated. In Experiment I, the amount of time 67 students reviewed their graded quizzes was determined. Results indicated that 63% of the students did not review their graded quizzes, suggesting students do not use the corrective written feedback provided on graded quizzes. In Experiment II, the effects of written corrective feedback versus scored feedback in terms of student performance were evaluated. The students in the experimental group received written and scored (points only) feedback on their graded quizzes before proceeding to the next targeted quiz. Probe quizzes were given to both groups. Results indicated that students in the control groups spent the same amount of time observing their graded quizzes as did the experimental group, suggesting that proctor written feedback was more effective than scored written feedback for enhancing student performance in this PSI course. (Author)