A study was undertaken in six fall 1978 courses at a large midwestern university to examine possible biasing influences on student ratings of instruction brought about by pre-course expectations of the course. Student and course demographic variables were analyzed as possible determiners of affective entry into the course. These data were examined for influence on student ratings of instruction. It was asked whether or not evaluations are more influenced by student expectations than by student background or course circumstances. Finally, data were examined for bias due to these out-of-class factors versus attitude change due to instruction. It was found that students brought to the courses expectations for and opinions about the instructor and course. These levels of affective entry were created or influenced by several student and course characteristics. Higher grade level students more often brought positive expectations of course and instructor. Electives or courses in the students' major field tended to contain students with high expectations. Pre-course gossip about courses also tended to be more positive than negative. Results suggest that faculty are in greater control of student evaluations than are the pre-course opinions of students or the demographic characteristics of the students or course. A list of references and statistical tables are appended. (MSE)