The science teaching self-efficacy beliefs of primary school teachers influence teaching practice. The purpose of this research was to determine if informal education institutions, such as science centres, could provide professional development that influences the science teaching self-efficacy beliefs of pre-service and in-service primary school teachers. A cohort of eight final-year pre-service teachers and 13 in-service teachers in Australia participated in this research over a period of 18 months. The results of this research showed that four hours of professional development workshops produced by science centres were capable of increasing the science teaching self-efficacy of all but three participants, with observable effects for at least 11 months after the completion of the workshops. The participants identified the workshops as a positive influence on their science teaching, and an important source of confidence and motivation. This project showed that the informal education sector can contribute to achieving positive reforms within science education, but only if the context in which teachers must operate is taken into account and reform efforts adapted accordingly. The informal science education sector could be the key to achieving long lasting reform in science education where other, formal measures have failed. Further studies are required to look at how places like science centres and museums can work with teacher educators, particularly in universities, to assist in the training of new teachers in science.