Over the last two decades, research has reached the conclusion that educator teamwork is necessary to ensure the achievement of school goals. No attempts, however, have been made to provide integrative evidence regarding its contribution to school effectiveness. To fill this void, the authors review two decades of professional team research in the context of schools. Specifically, the article has two objectives: (1) To review the existing conceptualizations of the terms 'team' and 'teamwork' in the school context; (2) To provide a systematic review of the impact of teamwork on school effectiveness. The systematic search resulted in 23 papers reporting three non-empirical and 20 empirical studies. The results of the review revealed a lack of agreement concerning the conceptualization of the terms 'team' and 'teamwork', which may affect comparability among studies. Furthermore, no comprehensive picture emerges regarding the consequences of teamwork for the individual teacher, the team, or the school as a whole. Indeed, studies refer to a wide range of variables within different contexts and configurations. This review contributes several important insights that may set the agenda for the next wave of research on teamwork in schools.