There is a persistent and significant gap in the achievement of students who attend high-poverty schools and those who attend low-poverty schools. Students in high-poverty schools, the majority of whom are African American and Hispanic, are not achieving the same levels of academic success as their low-poverty or White counterparts. Retention rates, graduation rates, and standardized test scores demonstrate a vicious cycle of reproduction by race and economics. Despite decades of reform efforts purporting to address this issue, little has changed for the better in the equitable education of students. Internal conditions often hinder the success of many high-poverty schools, including high teacher and administrative turnover, an excuse-driven culture, and ineffective operations. In our current policy context, schools are held accountable for their students' progress yet given little guidance regarding how to improve when such internal obstacles are present. As a result, failing schools remain failing and almost all of them are high-poverty schools. School reform relies on the internal ability of schools to respond to changing students and changing demands, but study of how whole-school capacity is strengthened for demonstrated student achievement is still only limitedly available. This study examines this issue and addresses this gap through a case study of successful internal reform in one high-poverty elementary school. Grounded theory methods of data collection and analysis were used to retrospectively examine this school's changes over time. Research questions focused on the what, how, and why of the changes to develop an explanatory theory of internal school reform. Findings indicated that the previous context of the school was hostile, instructionally complacent, and stagnant. With the entrance of a new principal, the school engaged in five processes of change that strengthened their internal capacity: taking immediate action, valuing and empowering teachers' voices, changing pedagogy, creating structures to systematize processes, and negotiating external initiatives. These processes together resulted in a transformed culture of collective responsibility, pervasive use of data, and continuous innovation, as well as school-wide achievement. The five processes are described and paired with several theoretical assertions regarding internal school change. [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.]