A growing body of evidence indicates that students can learn successfully by teaching, even when they do not receive any training in teaching skills or have substantial guidance on how to teach. To explain why acting as a teacher in one’s own way works effectively, this paper develops the role theory of peer tutoring and proposes a role hypothesis for learning by teaching. This hypothesis consists of three basic postulates. First, students have some teacher-role expectations in their long-term memory. Second, students who are assigned to the role of teacher have an awareness of being a teacher, which activates their teacher-role expectations. Third, the students are induced to enact the role of teacher in accordance with the activated teacher-role expectations. Their teacher-role enactment involves the effective processing of to-be-taught information to varying degrees, thereby fostering their learning. The findings of research on learning by preparing to teach or teaching are reviewed to assess the validity of the role hypothesis. Finally, some directions for future research are discussed.
