The expectation that educators will use data in the service of school improvement and planning is a major feature of national and local reform agendas. Prior research has found that the principal plays a critical role in making policymakers' visions for data use a reality at the school and classroom levels. Most prior studies, however, have not fleshed out how the principal functions as a key agent in influencing other key players in data use. This article will illustrate the actions of the principal, teachers, students, and district personnel through simulation models of principal leadership that we developed based on a case study of a high school implementing this reform. We use these models both as a framework for understanding our findings and as a way to enhance understanding of the processes by which educational reform is co-constructed through the simultaneous mediation of the multiple agents involved in the system. (Contains 6 figures and 1 note.)