This study examined first-year primary student teachers’ perceptions about teaching science and the vocabulary used in primary science. The study utilised a questionnaire to examine students’ perceptions before they had received any formal science education instruction at the tertiary level. Perceptions of students’ self-competence to teach primary science was related to their perceptions to explain selected vocabulary used in primary science. Similar relations existed between their explained meanings of the vocabulary and their ability to explain selected phenomena. There was a weaker relationship between students’ perceived ability and actual performance. Interviews were used to explore their perceptions, understandings and explanations. Students’ uses of oral genres were examined. Finally, areas of greatest assistance in developing students’ further understanding of science were identified.