This study emerged from a consideration of how some beginning primary school teachers cope when faced with teaching science. Primary teachers typically lack science content knowledge and therefore the science pedagogical content knowledge (PCK) that enables them to teach science. Aspects of a group of beginning primary school teachers'' science teaching practices were consequently examined in order to understand better the basis of their practice. In particular, science PCK and its relationship to activities that work were considered, illuminated by findings about activities that work from a separate study with practicing teachers. The main assertion arising from this study is that activities that work have a close relationship with science PCK. A number of implications for primary science curriculum emerge from this assertion, such as considerations for preservice teacher education science courses and the nature of the primary science curriculum.