Purpose: Research on educational leadership underscores the importance of principals operating as instructional leaders and intensive job-embedded supports for such work; this research also identifies central office staff as key support providers. However, it teaches little about what central office staff do when they provide such support and how to distinguish what they do as more or less supportive of principals' development as instructional leaders. This article addresses that gap with findings from an in-depth comparative case study of the work practices of executive-level central office staff in three districts dedicated to providing instructional leadership support to principals. Research Design: The conceptual framework drawn from sociocultural and cognitive learning theories identifies practices that deepen professional practice in authentic work settings. Data came from 283 interviews and approximately 265 observation hours and 200 documents. Findings: Departing from other studies that do not empirically elaborate central office work practices or that call generally for central office leadership, this analysis identified specific practices of central office administrators consistent with helping principals learn to strengthen their instructional leadership. These practices anchor a conception of central office staff in these roles as teachers of principals' instructional leadership. Key mediators of their work included their own conceptions of their roles and their opportunities to consult with colleagues, among other conditions. Conclusions: Advancing such work in practice and building knowledge about it in research will require significant shifts throughout school district systems and new approaches to the study of educational leadership. (Contains 7 notes and 1 table.)