This case study aims to reveal how conceptualization of native speakership was constructed and reinforced in a South Korean university classroom of English as a foreign language (EFL). In addition, it examines how this conceptualization positions native speakers, a non-native EFL teacher, and learners, and what learning opportunities were provided in this classroom. The participants of the study were one instructor and his students. The data include classroom observations, interviews with the teacher and students, and student surveys. The findings indicate that the students had been exposed to American English more frequently than any other English variety. Also, they wanted to learn American English in and outside of the classroom. Furthermore, this study shows that American English norms were revealed in the teacher's beliefs and reinforced in his classroom through his instructional materials, classroom practices, and evaluation of the students. Thus, as a mediator between native speakers and learners, the teacher positioned native speakers as authoritative possessors of correct pronunciation and expressions for his students to imitate. Consequently, the students learned about pronunciation and informal expressions as modeled by American native speakers rather than learning to use the L2 communicatively as recommended by the institutional policy. This study has important implications for English language teaching in South Korea, specifically in terms of the concepts of native speakership, student learning, and teacher education.