This study attempts to explore the nature and the potential of various discourse structures and linguistic functions that may facilitate students' learning in English classes co-taught by a native English-speaking teacher (NEST) and a local English teacher in Taiwanese elementary schools. Considering the nature of the study, the author employed a case-study approach to investigate the classroom discourse. In the study, data were analyzed based on a theoretical framework combining discourse analysis schemes, systemic functional theory of language, sociocultural theory of mind and activity theory. The study reveals that repetition drills were commonly used in the classrooms in spite of the difference in the learners' levels, and the Initiating-Responding model was the dominant feature of the classroom discourse structure. The target language, i.e., English, was used by the teachers for demanding information or action, while by the students it was used for repeating and imitating. In light of the findings, the author makes suggestions on co-taught English classes of this kind, for instance, the necessity of creating interactional context for language use, encouraging individual responses from students, and using alternative discourse strategies.