In winter 2014, I came upon an opportunity to conduct a case study on a team of middle school math teachers who initiated a study group to examine how a set of learning progressions could help them with their planning, instruction, and assessment. Learning progressions are research-based hypotheses about how students develop more sophisticated understanding of a topic. Educators, researchers, and policymakers have recognized the great promise of learning progressions for helping teachers conduct formative assessment in their classrooms by helping them to identify learning goals, elicit and interpret student thinking, and determine what instruction and feedback to provide to help students continue to make progress. However, the ways in which learning progressions can support teachers are not fully understood, and this topic provides a fertile ground for research. In this article, I describe the methodology I used in the case study which was guided by the literature on best practices in conducting case study research. I introduce key strategies for analyzing case study data to strengthen the internal validity of the results, including identifying a theoretical proposition, identifying and ruling out rival hypotheses, pattern matching, and triangulation. Finally, I describe the practical challenges I encountered regarding data collection and data analysis and offer some lessons learned.