["TESOL Quarterly, EarlyView. ", "\nAbstract\nThis linguistic ethnographic multicase study examines how three Turkish‐American students (ages 6–11) navigate boundaries between home, heritage language school, and mainstream school environments. Grounded in social constructivist theory, the study investigates students' navigational strategies across these three interconnected educational contexts. Data collection included 11 semistructured interviews with students, parents, and teachers, complemented by 30+ hours of field observations across all three settings, with analysis following the five steps of linguistic ethnography and employing open, axial, and selective coding techniques. Findings reveal that students navigate epistemic culture (differences in topics, tasks, and knowledge construction) and language use (varying linguistic policies and practices) boundaries. Students employed three boundary‐crossing mechanisms—boundary interactions, boundary people, and boundary objects—to facilitate navigation between discursive spaces. The study introduces “boundary mediators” as a distinct category of boundary people who coordinate practices between educational environments. Translanguaging emerged as a dynamic boundary practice, enabling students to bridge linguistic divides and integrate knowledge across contexts. These findings extend boundary‐crossing theory beyond traditional dyadic models to account for complex triangulated relationships that emerge when multilingual students navigate multiple formal educational contexts simultaneously.\n"]