In this article, the authors describe a research project designed to explore the effects of science testing in Year 6 (age 11) in England and implications of the abolition of testing in Wales since 2004. The research was commissioned by the Welcome Trust in association with the ASE to inform representation to the House of Commons Select Committee on Education enquiry into testing and assessment. The findings of this research reveal a strong commitment among primary teachers to the development of pupils' science process skills through investigations and other practical activities as a means to understanding science concepts. However, revision and test preparation in Year 6 in England militates against this, resulting in a narrow science curriculum and a tendency toward didactic teaching strategies. Although, perhaps surprisingly, it is still too early to draw firm conclusions about the impact of changes in assessment procedures at Key Stage 2 on the teaching of science in Wales, there are clear signs that Welsh teachers are beginning to exploit opportunities for investigative science in Year 6. Participants in both England and Wales made it clear that there is a useful role for testing in science at Key Stage 2 to support teachers' summative assessments, but there was strong agreement that statutory test results should not be used as the basis of league tables.