The purpose of this study was to determine if there was a difference in how high and low performing elementary school districts use and analyze data to differentiate instruction, make changes to district/grade level curriculum, determine professional development needs, determine teacher effectiveness, and determine the use of school district resources. The study surveyed 38 Illinois elementary school district superintendents in Region 7 located in South and South West Cook County. The 2012 ISAT reading data from Grades 3-8 were used to determine the top and bottom 40% of performance. The data indicated there were statistically significant differences in how high and low performing school districts use data to differentiate instruction and how high and low performing school districts allocate resources to support the student assessment data system. High performing districts indicate that they use student work to pinpoint areas where students need help. They also indicated that they have a data collection system in place that provides staff timely and pertinent student achievement data and a system that provides staff the data needed to make instructional decisions. [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.]