Federal and state accountability obligates public schools to improve standardized test scores for students in certain grades and in certain content areas from year to year. In the name of school improvement district and campus level administrators implement professional learning communities (PLCs) and set expectations for data informed instruction as initiatives to improve test scores and increase student learning. The bulk of this work falls on teachers. Collaborative professional learning and data use is difficult work, and relying entirely on standardized test scores to make decisions is not necessarily best practice. This case study of an elementary school investigated teachers' perceptions of PLC experiences and collaborative data use and whether teachers valued these practices and possessed the levels of expertise and self-efficacy to engage in this work. The study aimed to answer three research questions: What do teachers think about using data in PLC experiences to inform their instructional practices and increase student learning? How do teachers describe their level of expertise regarding data-use knowledge and skills? How can school principals know that teachers possess the confidence and self-efficacy to apply data-use strategies effectively in their daily work? In exploring teachers' perceptions about PLC experiences and collaborative data use, I hoped to gain insight into what teachers valued and what levels of confidence they had regarding this collaborative work. I chose to conduct the study at the school where I am currently the principal believing that my findings would inform my practice as an instructional leader and believing my findings would inform other principals engaged in similar school improvement practices. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]