Data has played an important role in England's recent school improvement journey. The evolution of the approach has not been perfect but the National Pupil Database has become a vital tool for health checking the education system, driving accountability, directing education policymaking, and tracking the educational attainment of key vulnerable groups. Within the United Kingdom, education is a 'devolved' responsibility managed at the level of each of the four national jurisdictions: England, Northern Ireland, Scotland, and Wales. This report focuses on experiences in England, which is by far the largest of the four political units. The purpose of this report is to highlight some of the lessons learned and successes of the England national pupil data story. This report is based on the expertise and experience of its authors and draws on some relevant literature to support key points and provide illustrations. This report is intended to offer insights for policymakers in other countries where a national pupil level data system is being developed or refined. By sharing England's story the authors hope that others may be able to avoid some of the mistakes and unexpected consequences that were made in the last three decades of development in England. The report provides analysis of seven key lessons: (1) The school accountability system in England benefits from a data infrastructure of national tests and information about pupil characteristics, supported by technology; (2) English experience demonstrates the risks of an over-simplistic approach to school performance data; (3) In England, there has been an important and lively debate about 'value-added' measures which take into account the starting points of pupils; (4) There is a need for a national accountability system that evolves over time; (5) Accountability measures used in England have played a significant role in the development of school self-evaluation; (6) Schools can benefit from comparing their own students' performance with that of the national database through item level analysis; and (7) There should be an alignment between data-based support for internal school improvement and external school improvement through inspection.