This paper reports the relationship between four English primary teachers' understanding of the nature of science and their practice. Action research was included as a major part of the research design in order to explore the dialectical interplay between various factors at work in the teachers' practice. The influences of both tacit and espoused understandings of the nature of science were considered alongside the teachers' beliefs about education, teaching, and learning. These beliefs were found to be the determining factor in the teachers' decisions about classroom strategies. In arguing for a dialectical perspective on teachers' practice, the research suggests that teachers' espoused understanding of the nature of science may also be at least partially formed by the influence of these beliefs, raising the possibility that influence may run from teaching to theoretical understanding and not the other way round. (Contains 5 tables.)