Schools are required to meet a range of students' learning needs and effective school leadership is needed for the implementation of pedagogical practices responsive to the challenges of increasing student diversity and academic accountability. Literature on differentiated instruction and its constituent elements suggests differentiation results in improved student engagement and academic progress (Tomlinson et al., 2003). Researchers who study change leadership and effective school leadership propose specific actions that school leaders can take to implement and maintain instructional innovations, such as developing a vision, delegating leadership, committing resources, and honing knowledge of instructional practices (Kotter, 1996; Louis, Leithwood, Wahlstrom, & Anderson, 2010). This case study sought to illustrate how an elementary school principal developed an understanding of differentiated instruction and the specific actions taken to initiate and sustain the use of differentiated instruction among teachers. Embedded case studies described four teachers' perceptions of leadership to support differentiated instruction, their understanding of differentiated instruction, and classroom practices which reflect differentiated instruction. Interviews and observations were completed with all participants and served as the primary source of data. Documents and related artifacts were collected when relevant. Findings indicated that the school leader's support for sustained professional development was critical for the implementation of differentiated instruction. The professional development occurred through a variety of modes, was situated within the school, and allowed for coaching and peer observation. The execution of differentiated instruction was bolstered by provision of common teacher planning periods, shared leadership with teachers, and the practice of coaching. The school leader developed an understanding of differentiated instruction based on students' readiness and learning styles through concurrent participation in professional development with teachers. The principal's understanding and teachers' practice of differentiated instruction were predicated on formative assessment to plan for instruction, teachers as facilitators of learning, and high student engagement. Implications of the study suggested that differentiating instruction based on students' readiness for learning is consistent with the current climate of instructional accountability. Providing opportunities for teachers to view differentiated instruction in practice assisted in a richer implementation by teachers, while continuous professional development, coaching, and common planning time sustained the initiative. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.