Current research into data use suggests that the intersection of assessment, reform, and public accountability and their impact on teacher practice are under-conceptualized and not well researched, especially when the data are derived from assessments that are locally produced by teachers. This qualitative case study investigates the development and use of local assessments in public schools in order to better understand how the act of creating local assessments and using data derived from local assessments influences teacher practice within the current state accountability policy environment. The conceptual frame and methodology of the study draw from existing literature on data use, teacher agency, as well as sense making theory. In particular, data use literature and sense making theory view teacher practice and teacher agency as situated in social and institutional contexts. Data for this study are derived from a year-long study of small groups of teachers in one suburban New York district who are engaged in professional development to develop and use assessments to inform their practice. The teams were trained through the Performance Assessment Design Initiative (PADI) where they developed learning objectives, rubrics as well as pre- and post-assessments based on state and local standards. The data in the study include assessment materials, non-participant observations, and individual interviews of teachers and team facilitators. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]