Leaders play a vital role in how data is used to inform school improvement, but little is known about how they both develop their espoused theories about data use during leadership preparation and then refine those ideas when moving to practice and theories-in-use. This article uses longitudinal qualitative data from interviews with participants in alternative leadership preparation programs in New York City. Our analysis led us to two dimensions of data use central to leaders’ approach: leader-driven vs. leader-facilitated data use and highly structured vs. flexible data use, and demonstrates common shifts toward more leader-driven and highly structured approaches.