This study seeks to describe how elementary principals in a large Washington school district perceived the district office administration's implementation of Response to Intervention over a four-year period. RTI is a widely used intervention system that requires schools to assess whether each of their students is learning, adapting instruction for those who are not, and continually reassessing and, when appropriate, re-adapting instruction. A case study, interview-based, action research methodology with data collected from interviews, principal professional learning communities, meetings, and professional development plans and programs were used to explore the perceptions of 14 elementary school principals as they reflected on the RTI implementation process over four years. It was my charge as the assistant superintendent to lead, assess, and refine the implementation process with the principals involved in this study. The principals generally agreed that the following facilitated program implementation: overcoming resistance to change, developing a widely shared vision for RTI, the identification of specific yearly stages of implementation, providing a professional development program aligned with the stages, providing feedback on performance with formal and informal assessment, the complexity and sophistication of RTI, the development of PLCs, the importance of the instructional coach and teacher leaders, and coordination with Title I and Special Education. [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.]