Policy problems do not exist as social fact awaiting discovery. Rather, they are constructed as policymakers and constituents interpret a particular aspect of the social world as problematic. How a policy problem is framed is important because it assigns responsibility and creates rationales that authorize some policy solutions and not others. This article brings together sense-making theory and frame analysis to understand the dynamics of problem framing during policy implementation. Data were derived from a yearlong ethnographic study of one school's response to the California Reading Initiative. Results showed that the school's response depended on how school staff constructed their understanding of the relevant problem to be solved. The problem framing process was iterative and contested, shaped by authority relations and mediated by teachers' social networks. Ultimately, it proved important for motivating and coordinating action, reshaping authority relations, and influencing teachers' beliefs and practices. (Contains 6 notes.)