In August 2000 the New Zealand Minister of Education announced, as part of a broader national assessment strategy, the development of exemplars of pupils' work at curriculum levels 1-5. The strategy is based on the conviction that assessment must make a difference to pupil learning. A team of primary science educators from across New Zealand participated in a collaborative project to develop the science exemplars. A number of significant issues, dilemmas and developments have arisen throughout the development of the project. Each of these issues needs addressing and will continue to be discussed as the implementation of the exemplar project proceeds. The final outcome of the project will be a set of science exemplars and matrices that can be used by teachers to develop the knowledge and skills to provide quality formative feedback to their pupils. This should enhance the quality of teaching, learning and achievement in science education in New Zealand schools at levels 1 to 5. (Contains 2 figures.)