This design case describes design decisions and their impacts during three redesigns of an educational game called the "Rocks and Minerals Challenge." This game was developed as a laboratory supplement for the rocks and minerals component of a university-based geology course. The game has evolved through three distinct design phases: Design 1, first designed as a challenge module in 2005; Design 2, redesigned as a game in 2012 for compatibility reasons; and Design 3, redesigned in 2015 to enhance instructional effectiveness. Following is a description of the game design factors that were implemented for each of the design phases: learning goals, levels of challenges, scaffolding, user control, feedback, and rules. The timing, rationale and impacts of these design decisions are discussed within the context of recommendations identified by existing educational game research.