A Korean science teachers' discursive practises were examined with a view to identifying pedagogical roles performed through his talk. Data came from the video recordings of classroom sessions where students presented their science projects and exchanged questions and answers during the presentations. Transcripts were developed and analysed in a qualitative way that identified the teacher's pedagogical roles to help students in the learning process. Three major discursive roles were defined, including making scientific knowledge available to students, coaching students to manage and enhance their performance, and scaffolding. Nine subordinate roles are also identified. Educational meanings of these teacher roles are elaborated upon, and implications for better teaching practises in the science classroom are discussed.