Purpose: We explored the practices and understandings around using disaggregated data to inform instruction of 18 principals from three Midwestern school districts. Research Method: This qualitative study used one-on-one semistructured interviews with the principals focusing on how they disaggregate data in practice. The protocol included general questions about principals' data practices as well as specific questions around disaggregation. Initial inductive coding began with principals' direct responses to specific questions around disaggregation, and then emerging themes were used to analyze the entire transcripts. Findings: Participants were more likely to talk about disaggregation in relation to performance (by teacher, by grade level, etc.) than by subgroup (by race/ethnicity, by gender, etc.). Further analysis highlighted principals' purposes for disaggregating data that focused on identifying low performance on standards-based assessments, as well as the challenges they faced, particularly in terms of technical skills and software. Implications for Research and Practice: We conclude with a discussion of how disaggregation could support or challenge equity-focused leadership, with implications for policy, practice, and preparation. We consider the role of the principal in identifying inequitable patterns versus focusing on individual students, and different ways that equity can become part of regular leadership practice.