The current interest in using data-driven decision-making in schools has focused on how best to use student achievement data to meet the demands of current accountability requirements. The purpose of this study was to investigate promising practices specific to school leaders' use of data-driven decision-making for school improvement at two California charter schools. The following data sources were included in this qualitative case study that applied descriptive research and design: interviews of charter school principals and other administrators, interviews with teacher leaders, review of archival documents, and observation of professional development meetings related to the use of data to influence teaching and promote student achievement. The case study answered the following questions: How do charter school leaders use data for decision-making and school improvement? How are resources allocated to effectively implement the use of data for decision-making and school improvement? What challenges have charter schools faced in implementing the use of data for decision-making and school improvement and how were they addressed? What evidence exists that the use of data for decision-making resulted in positive educational outcomes? The study found that the greatest impact of using data-driven decision-making was on results of high student achievement and on the improvement of teaching strategies to meet student needs. By establishing a strong data-driven school culture, daily classroom observations, professional development, and providing teachers with ongoing support, school leaders experienced a profound impact on student achievement. In order to implement the effective use of data-driven decision-making the findings suggested several practical strategies. First, the total school community (parents, students, teachers, school leaders) had a common understanding of how data was used and analyzed to meet individual student learning needs. Additionally, the principals and other school leaders embraced the data-driven decision-making process, had strong skills in curriculum and instruction, provided ongoing professional development, and analyzed data with connections to improved teaching strategies and improvement of student achievement. Classroom visits were conducted on a daily basis allowing principals to provide immediate support or model a lesson if necessary. Finally, a culture of trust and collaborative inquiry was established where teachers were able to learn, question and share the relationship between data and good teaching practices. The findings of this study have been incorporated into the Center on Educational Governance Web-Compendium of Promising Practices designed to disseminate innovative best practices beyond the school site and assist other policy makers and educators who wish to gain knowledge on leaders' use of data-driven decision-making for school improvement. [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.]