This article considers lessons learnt through involvement in several assessment projects. Early experience, in university work and in school examinations, led to an opportunity to help establish a novel system of assessment for an innovative school curriculum. Different lessons were then learnt from work on a national survey of school students' learning of science, and different lessons again while leading a group to advise the UK government on a new scheme for national testing of all students. Many welcomed the group's advice but politicians rejected it; however, the recoil from this defeat led to very rewarding work on formative assessment. The article ends with reflection on the conflict between the summative and the formative and ways to resolve that conflict, along with the full benefit of formative approaches that investment can secure to help teachers share responsibility for high-stakes summative assessments.