Research on learning by teaching has mostly focused on the learning effects of teaching after preparing individually to teach. This study investigated the impact of preparing collaboratively (versus individually) to teach on learning by teaching. Japanese undergraduate students (n = 96) provided instructional explanations on video or listened to their partners' instructional explanations after they had studied learning material for teaching in collaboration with their partners or had done so individually in the presence of their partners. Participants who prepared collaboratively to teach provided higher-quality instructional explanations on video and learned better by teaching than those who prepared individually to teach. The quality of the videotaped explanations significantly predicted the outcomes of learning by teaching. Whether after collaborative or individual preparation, there were no significant differences in learning outcomes between those who explained on video and those who listened to their partners' explanations. These results suggest that although the learning effects of providing and listening to instructional explanations may be comparable, is more beneficial to learning by teaching than individual preparation.