The purpose of this study was to inform instruction by using data as a progress-monitoring tool to drive instruction and ultimately student achievement. During the course of this study, data was gathered from a pre-test in a mathematics measurement unit to determine differentiated instruction and grouping. Formative short frequent assessments were applied to monitor the learning progress of all students in a fourth grade inclusion classroom. Data was used to change instructional strategies, grouping, and teaching methods to ensure learning success on the unit post-test, and ultimately on end of the year testing. Results demonstrated that by incorporating methods of research-based instruction and implementing short frequent assessments, teachers could begin to bridge the gap in achievement for all learners. Monitoring student progress throughout the school year can inform teachers of the individual learning needs of their students. Teachers can use the data to measure the learning strengths and weaknesses, so that student performance can be analyzed and evaluated. The gap in achievement can be overcome using the implementation of targeted strategies and research-based interventions for all students. Appended to this document are: (1) Appendix A: Student Achievement on Summative and Formative Assessments; and (2) Appendix B: Vassarstats Calculations. (Contains 1 table and 1 figure.)