This article discusses a framework for the analysis and assessment of twenty-first-century language and literacy practices in game and design-based contexts. It presents the framework in the context of game design within "Gamestar Mechanic", an innovative game-based learning environment where children learn the Discourse of game design. It identifies three dialogic interactions (the material, the ideal player and the real player dialog) that a student must participate in in order to effectively learn the meaning production and interpretation practices germane to good game designs. These dialogs provide the syntactic, semantic and pragmatic components necessary for students to gain fluency in the game designer Discourse. The article illustrates the framework in practice by analyzing two language samples collected in an after-school game design workshop structured around "Gamestar Mechanic." Its implications for the research and assessment of game-based learning environments are discussed. (Contains 7 figures and 2 tables.)