This study examined how midterm student ratings feedback provided to teaching assistants via a theory-based ratings instrument, combined with consultation on instructional practices, would affect teaching practices, ratings of teaching effectiveness, and student learning and motivation. The student ratings instrument that was employed focused on a series of instructional activities derived from Gagne's theory of instruction and Reiser and Dick's instructional model. Thirty-seven teaching assistants in undergraduate computer science and chemistry courses were randomly assigned to either a feedback + consultation group or a no-feedback group. Results of this study indicated that the feedback and consultation process had a significant impact on instructional practices and ratings of teaching effectiveness. Student learning and student motivation were positively correlated with the frequency with which the various instructional activities examined in this study were utilized. Implications of these findings and suggestions for future research are discussed.