A persistent and pervasive disparity in academic achievement exists between ethnic minority and English Learner students and their White and Asian peers. This qualitative single-case study of a high-poverty, high-performing middle school focused on the cultural norms, practices, and programs that were perceived to be contributing to narrowing the achievement gap. Through interviews, observations, a survey of certificated staff, and review of school documents, the factors that were perceived to increase academic performance of Hispanic, low-income, and English Learner students were explored. The cultural norms of a compelling mission of inclusion, equity and access, high expectations, shared leadership, and collaboration were perceived to contribute to narrowing the gap. The practices of data analyses, standards alignment of curriculum, instruction, assessment and grading, school-wide instructional strategies, consistently enforced discipline practices, and strong student/staff relationships were perceived to contribute to narrowing the gap. Programs at the selected school were perceived as only moderately contributing to narrowing the achievement gap. A significant percentage of school staff, united by a compelling mission and provided with access to current accurate student achievement data, collaborate to develop solutions that address learning needs of students. Sustaining practices included intentional acculturation of new staff members to believe in a compelling mission, district office support and goal alignment, and time reserved for collaborative data analysis. [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.]