This paper investigates the impact of a current educational policy initiative in Singapore called "Science Practical Assessment" (SPA). SPA is designed to overcome the limitations of single, high-stakes examinations by placing emphasis on research processes, entrepreneurship and the development of science practical skills. Structurally, SPA repositions teachers as central in the selection of items to teach and assess during the academic years leading up to O-level. However, it is contended that the effectiveness of SPA is rendered problematic without specific attention being paid to teachers' readiness and capacity to understand and implement assessment innovations. In response, the author describes and analyses how he formed a research partnership with a local physics teacher to investigate how SPA could be used as a tool to improve science pedagogy. Results suggest that while the pragmatic considerations of assessment reforms are not sufficient in themselves to bring about policymakers' desired outcomes, ways can be found to help teachers prepare for, bring about and crucially own change by adopting a critically reflective stance on problems and issues that arise when students work on completing laboratory tasks. The methods used in this study also identify some of the factors that impact on teachers' ability to influence positive developments at the department and school levels of an educational system. Overall, the intention is that the teacher development strategies and classroom practices illustrated in the paper will eventually inform a programme of interventionist action in science pedagogy and practical work assessment with applications both in and beyond the immediate study context. (Contains 1 figure and 5 notes.)