Data-informed decision making is an educational construct developed to meet No Child Left Behind mandates for improving education. Researchers have examined institutional best practices, but relatively little has been said regarding the individual practices of teachers as they implement data use in the classroom. The purpose of this study was to determine how teachers in one elementary school use assessment data from Scott Foresman's reading curriculum, Reading Street. The qualitative case study approach was used to develop an understanding of how teachers are using student data, which is necessary in determining plans of action and training regarding teachers' use of data in the classroom. Results suggested that teachers feel most effective when data use is time-efficient, allows for formative assessment, enables adaptation, and remains accessible. Classroom teachers implemented Reading Street data in multiple aspects of the classroom, to determine practice, improve remediation, display accountability to leadership, and demonstrate student improvement. The Continuous School Improvement (CSI) team was determined to be an essential support, as was leadership's focus on allowing classroom flexibility within the confines of school standards and goals. Barriers included the lack of training related to the effective use of the Reading Street program and resources, and lack of alignment between Reading Street curriculum and system-wide standards. The study's findings provided information that can advance teachers' effective use of Reading Street assessment data, illuminate supports essential to teachers' effective use of Reading Street assessment data, and reveal barriers that thwarted teachers' effective use of the data.