In the service of educational accountability, student achievement tests are being used to measure constructs quite unlike those envisioned by test developers. Scores are compared to cut points to create classifications like "proficient"; scores are combined over time to measure growth; student scores are aggregated to measure the effectiveness of teachers, schools, and school districts; indices are created to measure college and career readiness. These and other new uses rely on derived scores created to measure new constructs. The field of educational and psychological measurement has largely ignored these significant, consequential measurement applications. The conceptual frameworks and analytical tools of educational and psychological measurement should be used to study such derived scores and the validity of their uses and interpretations.