Data-driven decision making has become an important educational issue in the United States, primarily because of federal and state emphasis on school accountability and achievement. Data use has been highlighted as a key factor in monitoring student progress and informing decision making at various levels of the education system. Federal and state policies require educators to use data to inform decision making and the assumption is that educators already know how to analyze, interpret, and use data to make informed decisions. The purpose of this study was to gain a better understanding of classroom teachers' engagement in data-driven decision making practices at the micro level. Four research questions guided this investigation: (a) Why and how do select classroom elementary teachers choose specific data to inform their practice?; (b) How are data being used by these teachers to make instructional decisions?; (c) In relation to data use, what practices support instruction? What areas do these teachers seem to struggle with?; (d) What accounts for the variations in this select group of elementary teachers' ability to use and make decisions around data within and across schools? A qualitative case study/cross case analysis design was employed to study classroom teachers at two elementary schools in San Diego County. Interviews, classroom observations, and documents were used to compare and contrast findings within and across cases. The findings suggest that: (a) Teachers used a variety of data in different ways and for different purposes; (b) There were variations in teachers' capacities to engage in data-driven practices; (c) Contextual and cultural differences as well as differences in teachers' perspectives concerning autonomy and ownership of their work may have accounted for differences in teachers' capacities to use data. The findings from this research study have implications for district and school leaders who are intent on improving data use and promoting a culture of continuous learning. [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.]