Generalizability theory is used to examine the sources of variability present in a teacher and course evaluation instrument. Two studies were conducted. In the first study, four different forms commonly used by one specific college of a large midwestern university were examined using responses of 915 students. The analysis of variance performed on each form separately indicated that one form did not generalize well across students in comparison with the other three. In the second study, the performance of a five-item form across three levels of courses (734 students in undergraduate, intermediate, and graduate courses) in one specific college were examined. The course evaluations from graduate level students were found to be more reliable. In this case, evaluations of undergraduate level courses should not be considered as reliable and generalizable as those collected in higher level courses. (Contains nine tables and nine references.) (Author/SLD)