It is often argued that games have great learning potential. However, there only exist few empirical studies that describe the "messy" reality of teaching and playing games within an educational context. In order to get a better understanding of the relationship between game design, game pedagogy and game interaction, this design-based study explores the design and use of an ICT-supported debate game entitled "The Power Game" for Danish upper secondary education, where students assume the roles as politicians, spin doctors, and journalists in order to win a parliamentary election. Based upon insights from pragmatism, interactionism and dialogism, a theoretical and analytical model is presented that describes educational gaming as a dynamic interplay between different knowledge aspects. Through an ethnographically inspired approach to discourse analysis, it is demonstrated how teachers and students that participate in "The Power Game" create playful and unpredictable tensions between different ways of enacting and validating knowledge. These tensions imply important consequences for the ways in which educational games can and should be designed, taught, and played.