This report by Research for Action examines the use and impact of interim assessment data in Philadelphia's elementary schools, highlighting both the acceptance of these assessments by teachers and the complexities in attributing improvements in student achievement to their use. Despite teachers' satisfaction with benchmark data, the study finds that greater effectiveness in raising student achievement is linked to adherence to a core curriculum and benchmark assessments, with challenges remaining in leveraging data for deeper educational discussions. Recommendations for enhancing the use of these assessments include focusing on strong instructional leadership and teacher professional development.