Self-efficacy has been shown to be an issue of concern for primary teacher education students--many of them have low self-efficacy and this can negatively affect their future teaching of science. Previous research has identified four factors that may contribute towards self-efficacy: enactive mastery experiences, vicarious experiences, verbal persuasion and physiological/affective states. It could also be argued that there are additional sources of self-efficacy that apply to primary teacher education students, namely cognitive content mastery, cognitive pedagogical mastery and simulated modelling. The main purpose of the present paper was to investigate the relative importance of the various sources of self-efficacy in a primary science methods course. Data on changes in self-efficacy and sources of self-efficacy were collected throughout the course using formal and informal surveys. It was found that the main source of self-efficacy was cognitive pedagogical mastery.