Students' personal theories about education change as students gather new evidence about intelligence, learning, and knowledge. The present study investigated whether college instructors' play a role in changing students' personal theories with the messages professors send in the classroom. Students (N = 162) and instructors (N = 15) of undergraduate-level math and science summer courses completed surveys assessing personal theories about education and the frequency of messages related to educational beliefs. Multilevel models found that both between-class and within-class differences in reported messages corresponded with students' personal beliefs at the end of the course. Instructors' personal theories were generally not predictive of students' personal theories, and students' initial personal theories predicted the messages they remembered hearing.