EMI (English-medium instruction) is increasingly prevalent and is an important site in which students are introduced to academic English. Research into classroom interaction in EMI in schools has been limited. Recent research into classroom interaction in EMI in higher education (Basturkmen & Shackleford, 2015;McLaughlin & Parkinson, 2018) has drawn on the construct of language-related episodes (LREs) to investigate incidental instances during classroom interaction which is primarily focused on disciplinary content when attention shifts temporarily from content to language. The present article reports a study of LREs in two distinctive EMI, high school settings in South Korea. Analysis of recorded classes indicated that the occurrence of LREs was similar across both settings. LREs occurred frequently, focused mainly on disciplinary uses of vocabulary and were mainly teacher-initiated. Furthermore, the vast majority of the teacher-initiated episodes appeared to arise pre-emptively and not in response to errors, a finding that suggests the disciplinary teachers were proactive in shifting attention to language. Evolving content-driven discussion appeared to prompt the teachers to highlight the disciplinary register, and thus served as an impromptu, transitory means by which the teachers highlighted academic language use in their content teaching.