2020 Volume 68 Issue 4 Pages 401-414
Recent publications have proposed various hypotheses as to why learning by teaching is effective. The present paper classifies those theories on the basis of their hypothesized underlying mental processes into the following 5 categories: (a) a knowledge-construction hypothesis that proposes that preparing to teach and teaching stimulate knowledge-building and generative processing, thereby fostering learning, (b) a motivation hypothesis that proposes that acting as a teacher enhances motivation to process learning material in a knowledge-constructive manner, (c) an explanation-generation hypothesis that proposes that preparing to explain and explaining encourage knowledge construction, (d) a metacognition hypothesis that proposes that providing instructional explanations and interacting with students promote knowledge construction through the enhancement of metacognitive monitoring, and (e) a retrieval-practice hypothesis that proposes that the retrieval practice inherent in the provision of instructional explanations increases learning. The present examination of the results of prior research suggests that some evidence favors the knowledge-construction and metacognition hypotheses, whereas evidence relating to the other 3 hypotheses is highly limited or mixed. Finally, future directions for research are discussed.