The present study seeks to determine the variables explaining differences between the scores of student ratings given to instructors within the context of the university through discriminant analysis. Ratings given by students were grouped into two groups based on their means and instructors were labeled as low-rated and high-rated. Predictors identified by discriminant analysis are (i) class size, (ii) credit, (iii) grade level, (iv) mean grade, and (v) number of sections. Results of the study suggested that low rated instructors are those who teach courses with smaller number of students, lower credits, higher grade levels, higher mean grades, and one section. Identification of source of differences between ratings may provide invaluable information for those who are interested in assessment of instructional effectiveness.