The research in this dissertation examined the language and literacy practices of middle school children as they played Gamestar Mechanic, a game-based learning environment constituted by a flash-based multiplayer online role-playing game designed to introduce them to the Discourse of game designers, by exposing them to key principles and activities behind the production of good computer games. The dissertation begins by presenting the historical arguments behind the idea of design as a central mindset behind thinking, language and literacy practices that are becoming central for the effective social, civic and professional participation of learners in the 21st century. It provides a comprehensive review of the way in which the design of computer games has been used by educators and researchers in learning environments intended to foster some of these skills, guiding the initial design of Gamestar Mechanic. It then goes on to present an overarching discussion of the three years of the project, and how a design research agenda has served to guide the articulation of the game, its underlying learning theory and the gradual refinement of both based on the experiences of children in real learning settings. Using the findings that emerged from these three years, it presents a theoretical framework based on three dialogic interactions between designers, material game components, and player identities, which can serve as the guide for the analysis and assessment of language and literacy practices based on game design within the game. The last three chapters concentrate on each of the three dialogs applied to the analysis of children's play activities in game design workshops, and to the insights that emerged their language and literacy practices through a multimodal form of Discourse Analysis integral to the framework. It concludes with a discussion of the implications of project findings for educational practice and research. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]