This chapter focuses on game-based learning (GBL), and the way a commercial videogame was used to foster collaborative reasoning about morality and ethics in citizenship education. A high school class was video recorded for four weeks, and the data was analyzed to investigate how students collaboratively reasoned in the GBL situation. Post-interview data were also considered. The study found that collaborative reasoning was mediated both by the videogame and the dialogical interactions facilitated by the teacher. Students appropriated both bottom-up and top-down reasoning processes and positioned themselves to anchor practical and conceptual knowledge. This research proposes a learning model that describes the anchoring process as an important tool for promoting content understanding and collaborative reasoning in learning across contexts with GBL.