The game-based nature of teaching games for understanding means that teachers must be effective observers of game play in order to encourage thinking processes during game play, diagnose the performance problems of participants, and identify solutions. This article briefly reviews the teaching games for understanding (TGFU) approach and describes its implications for the role of the teacher. The primary purpose of the article is to provide a framework to help teachers understand the complexities of game performance, observe game play, and subsequently determine performance problems and appropriate instructional foci to alleviate the problems identified. (Contains 3 figures.)