This study examines what forms of data school leaders use, how they matter for students' learning, and which school contexts matter for such leadership practices to succeed. Utilizing hierarchical linear modeling, we analyzed survey responses from 1,381 school leaders and administrative data from 269 Florida schools. We find that although school leaders place the greatest emphasis on responsive data use to identify student needs, followed by the state standardized test, there are no linkages between these practices and students' performance. Conversely, leaders place the least emphasis on benchmark assessment data, yet this is the only type of leaders' data use associated with student achievement. Such beneficial leadership practice is more likely to occur in schools characterized by trusting relationships among staff. Altogether, these findings suggest that professional development in benchmark test usage for leaders and the cultivation of trusting organizational cultures are crucial for advancing the potential of data-informed reform.