No Child Left Behind mandates accountability data for school districts. This mandate has led to increased attention to instruction and academic remediation among educational researchers. The current study used schoolwide curriculum-based assessment (CBA) and curriculum-based measurement (CBM) data to plan and deliver mathematics instruction to examine if this would lead to improved student skill within one school year and improved group test scores between school years. The Screening to Enhance Equitable Educational Placement (STEEP) schoolwide problem-solving model was used in one elementary building, with CBM data used to track progress and CBA data used daily to track mastery at each skill level. Results suggested that children made significant progress within one school year, as measured by CBM, and the school significantly increased Stanford-9 mathematics scores after implementing the program. Potential implications for assessment and instructional practice are included.