Over the last decade educational games have become more and more popular. There are many games specifically designed as educational games, as well as a number of entertainment games that have been successfully used for educational purposes. The EduGameLab project aims to stimulate the use of games in the classroom. This paper presents a meta-analysis of the effectiveness of game-based learning and focuses specifically on empirical evidence on the effectiveness of using games in education in the last decade. Moreover, the study focuses on usage in formalized school contexts, i.e. pre-school, elementary school, secondary school, high school and higher education. As secondary aims we also assess whether there are any clear methodological trends and whether a link could be found between the outcome of empirical studies and the evaluator being a stakeholder in the game development.