A highly proficient Direct Instruction (DI) teacher is a teacher who is able to demonstrate the effective use of Direct Instruction curriculum and teaching practices, resulting in sustainability and high student achievement. In this qualitative case study investigation, I describe and, when possible, explain how two teachers reflected on the interactions among Direct Instruction curriculum, their teaching practices, and their beliefs to become highly proficient, sustaining DI teachers. These two highly proficient Direct Instruction teachers aligned the DI curriculum and teaching practices with their beliefs. Beliefs, this study found, had more to do with the teachers' self-efficacy, or beliefs in themselves, than about teaching, student learning and education in general. It was also found that sustaining a Direct Instruction implementation was not something that was achieved by teachers. Instead, it was a never-ending cycle of interactions among four key events: learning, achieving, believing, and enjoying. Leaders of Direct Instruction implementations must recognize that the ultimate goal of an implementation is not to solely change the teaching practices of the teacher, but to strive for sustainability. This requires on-going professional development and leadership. Hiring individuals with dispositions that would orient them toward a Direct Instruction approach to teaching could help accelerate the process, as does ensuring that entry-level efficacy is high through training and on-going coaching. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]