The researcher examined the implementation and use of assessment practices of teachers and administrators for school improvement efforts. This case study was conducted at an urban elementary school in a district in the southwestern region of the United States that has accomplished sustained growth on state summative assessments in English Language Arts and Mathematics for 5 consecutive years. The researcher used qualitative research, which included semi-structured interviews with tested grade level teachers and site administrators, as well as collected data from observations in fourth and sixth grade classrooms. Research questions addressed the use of formative assessments, data analysis, the role of leader, teacher, and student in the improvement process. Among the themes found in the study were a laser-like focus on student achievement, the use of data analysis from assessment to inform instruction, an alignment of best practices, teacher collaboration and support, as well as relationships. The findings suggest that the use of formative assessment positively impacts student achievement. The study further describes implications for educational leaders.