Abstract: This qualitative case study examined the code-switching (CS) produced by English Education students during peer interaction in a Public Speaking course at University of Mataram. Data were collected through two classroom observations of debate sessions involving twenty-five students and semi-structured interviews with ten purposively selected students, then analyzed thematically following Braun and Clarke’s (2006) framework, using Poplack’s (1980) typology and Cook’s (2001) functional categories. Nineteen instances of CS were identified from approximately 198 recorded utterances. All three types of CS proposed by Poplack (1980) were found, with intra-sentential switching the most frequent (11 instances), followed by tag-switching (7) and inter-sentential switching (4). All four functions proposed by Cook (2001) were also identified, produced almost entirely by the students themselves: the affective function was the most frequent (7 instances), followed by the interactional (6), pedagogical (6), and classroom management functions (3). Interview data revealed mixed perceptions of whether CS supported or hindered English learning, several informants felt it aided comprehension and vocabulary acquisition, while others felt it reduced opportunities to practice speaking fluency, with most informants, as prospective English teachers, favoring a limited and context-sensitive use of CS rather than a strict prohibition or unrestricted allowance. The study concludes that code-switching among EFL peers is a natural and functional part of classroom communication that requires a balanced, context-sensitive pedagogical response. Keywords: Code-Switching, EFL Classroom Interaction, Peer Interaction, Functions of Code-Switching, Qualitative Case Study.