In the Yonkers Public Schools district, teachers who are trained in data-driven instruction often fail to use their training to plan and deliver the instructional program. Identifying the reasons why this is the case from the teachers' perspective is important to district school leaders, school administrators, and teachers who desire to improve instruction. The purpose of this qualitative case study was to investigate the perceptions of teachers in regard to how they can more successfully use students' achievement data to improve instructional practices. Constructivism, connectivism, and data-driven instruction provided the theoretical foundation and framework for the 4 research questions. These questions were designed to glean information from teachers' experiences on how they use data to change instructional practices and how these practices facilitate the implementation of smaller learning communities (SLC). The administration of a confidential open-ended survey, a focus group interview, and a teacher-reflection protocol, as well as an examination of unobtrusive data, were the data collection strategies used to investigate the problem. Coding was the primary strategy for data analysis. The findings indicated that SLC teachers have a positive perception of the use of students' achievement data to plan and deliver the instructional program. The implications for positive social change include the effective use of students' achievement data to improve instruction, implementation of successful SLCs in urban schools, and ways to address student learning at the high school level that may result in more students who achieve at higher levels. [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.]