A persistent mathematics achievement gap between African American, Hispanic, and European American students at one elementary school was the focus of this investigation. The research questions of this single site case study involved understanding why an achievement gap exists, and to identify the instructional strategies and best practices used to narrow the achievement gap. Ecological systems theory was used as the conceptual framework to organize and classify data to explain the findings. Interview data from 14 educators, student test results, and documents (parent logs and campus action plan) were collected and analyzed over five weeks. Data analysis strategies included transcribing interview data, data triangulation, and identifying common themes to report the findings and conclusions of the study. Results of the study indicate that poverty, lack of parental involvement, student culture and behavior, student mobility, and a lack of consistent small group instruction contributed to the achievement gaps between African American, Hispanic, and European American students in mathematics. Likewise, findings indicate that the school narrowed the achievement gaps by actively involving school personnel, implementing small group instruction, encouraging teacher collaboration, mentoring students, and using a variety of resources. Thus, a complexity of factors contributed to the mathematics achievement gap, and a variety of instructional strategies and best practices aided in narrowing it. Recommendations include conducting further research on parents' and local, state, and federal leaders' perceptions of achievement gaps, and the development of an analytical framework for studying achievement gaps. Implications for positive social change include providing educators further insight to narrow achievement gaps, which can help promote equitable education for all students.