The case study summarized in this article relies primarily on activity theory (e.g., Engestrom, 1987), and incorporates complexity, accuracy, and fluency analyses (see Ellis & Barkhuizen, 2005) to describe real-time oral language production by four focal English language learners (ELLs) in a sheltered high school math classroom in the U.S. Further, it describes how that language use was influenced by the classroom context. Findings indicate that ELLs produced very little complex, elaborated academic language because there were a variety of contextual factors that interacted to minimize students’ need to use it. Insights gained from an activity theory perspective highlight the influence of three unresolved tensions in the classroom activity system, namely: low language expectations in the curriculum, the teacher’s lack of familiarity with L2 instructional strategies, and the students’ lack of engagement with “best” practices that included use of hands-on material. Greater administrator support and transparency about desired academic language outcomes could enhance both the teachers’ language development skills and student outcomes.