Adopting a longitudinal field study, this paper investigates whether entity theorists (students who believe human attributes are fixed) are less likely than incremental theorists (students who believe human attributes are malleable) to change their evaluations of a teacher in accordance with his behavioral changes. An instructor exhibited some forgetful behaviors in the first half of a course, and ceased doing so in the second half. Consistent with our hypothesis, incremental theorists adjusted their perceptions of the instructor. They rated him as less forgetful accordingly at the end of the course than at the middle. Entity theorists, however, did not show this change. With improved ecological validity, this study extends previous laboratory studies to teacher evaluation.