Evolving impressions: undergraduate perceptions of graduate teaching assistants and faculty members over a semester.

Undergraduate experiences in lower-division science courses are important factors in student retention in science majors. These courses often include a lecture taught by faculty, supplemented by smaller sections, such as discussions and laboratories, taught by graduate teaching assistants (GTAs). Given that portions of these courses are taught by different instructor types, this study explored student ratings of instruction by GTAs and faculty members to see whether perceptions differed by instructor type, whether they changed over a semester, and whether certain instructor traits were associated with student perceptions of their instructors' teaching effectiveness or how much students learned from their instructors. Students rated their faculty instructors and GTAs for 13 instructor descriptors at the beginning and near the end of the semester in eight biology classes. Analyses of these data identified differences between instructor types; moreover, student perception changed over the semester. Specifically, GTA ratings increased in perception of positive instructional descriptors, while faculty ratings declined for positive instructional descriptors. The relationship of these perception changes with student experience and retention should be further explored, but the findings also suggest the need to differentiate professional development by the different instructor types teaching lower-division science courses to optimize teaching effectiveness and student learning in these important gateway courses.