Despite the prevalence of case-based reasoning in systems design, many of the established design principles are based on theory rather than empirical studies. This study describes the evolution of a case library learning environment and its transition to a game-based learning approach using educational design research (EDR). We discuss our iterative processes of design and development and situate these processes within the broader framework of educational design research. We discuss how the earlier versions of the problem-based learning environment were based on design principles extracted from case-based reasoning theory. Subsequent studies caused us to rethink the intersection of theory and design, along with its impact on learning outcomes. Using a variety of data collections (e.g. analytics, causal maps) and EDR strategies (e.g. conjecture maps), we identify the following new design principles based on CBR theory: emergent design principles that focused on optimal case length, mechanisms to prompt case retrieval and decision-making, and visual presentation. Implications for problem-based reasoning, case-based theory, and interface design are discussed.