Games for Change (G4C) is a movement and community of practice dedicated to using digital games for social change1. However, a common model of persuasion built into most G4C, called Information Deficit, assumes that supporting children to learn facts will result in behavior change around social issues. There is little evidence that this approach works. We propose a model of game play, called Emergent Dialogue, which encourages children to discuss their values during interaction with factual information in a G4C. We summarize a set of guidelines based on our Emergent Dialogue model and apply them to the design of Youtopia, a tangible, tabletop learning game about sustainability. Our goal was to create a game that provided opportunities for children to express and discuss their values around sustainable development trade-offs during game play. We evaluate our design using video, survey and questionnaire data. Our results provide evidence that our model and design guidelines are effective for supporting value-based dialogue during collaborative game play.