This project explored the free school meals (FSM) measure in the National Pupil Database, and its use in research, policymaking, and practice. For years, FSM has been a core measure of child and family circumstances, used by analysts and academics, within government, by services and practitioners, and within schools. It has been used to identify children for targeting and interventions, to allocate funding and resources, to evaluate policies and educational systems, and for accountability purposes. It has been used to proxy disadvantage, deprivation, and family circumstances in research. Given the prevalence and multidimensionality of the uses of FSM, including for many high-stakes purposes, it is important to understand it more deeply as a measure.