Background: Validity is a central concern in any assessment, though this has often not been made explicit in the UK assessment context. This article applies current validity theorising, largely derived from American formulations, to national curriculum assessments in England. Purpose: The aim is to consider validity arguments in relation to the multiple purposes which national curriculum assessments serve. This is because validity is now understood in terms of how the test results are interpreted and used. Multiple purposes mean multiple uses of the results, each requiring justification. Sources of evidence: A validity framework for national curriculum assessments is presented which is organised around purposes, fitness-for-purpose, reliability and the interpretation and impact of the results. Current tests are evaluated against this framework. Main argument and conclusions: The analysis finds the national test regime successfully meets some of the common threats to validity. The main concerns are about the multiple high-stakes purposes for which the tests are used and their impact on teaching and learning. Some alternative approaches are then considered, which could reduce the burden of interpretation which the tests currently bear. (Contains 1 table and 7 notes.)