Computer tutorial review lessons for a one-quarter lecture course in introductory college physics have been developed and used by approximately 500 students, on a voluntary basis, over a period of several years. The investigation reported here shows that the exam grades of students who used the computer materials are significantly higher (.01 level) than the class as a whole, if results from sections are pooled. Evidence is presented to show that the results are not primarily due to a factor of selection because of the voluntary basis for participation. (Author/JK)