In this article, we investigate translanguaging in an English/Spanish dual language, urban, middle school science classroom as the teacher and students employ a scientific argumentation framework to address biodiversity socioscientific issues. Drawing from theories of sociocultural psychology and sociolinguistics, we considered how engaging in scientific practices was constructed through concerted activity by a bilingual teacher and her emergent bilingual students across English and Spanish language practices. Using ethnographically informed data collection in conjunction with discourse analysis, teacher translanguaging was examined for its related functions in the science classroom and how this pedagogical practice afforded opportunities for framing and supporting scientific argumentation. Results suggest that the functions of teacher translanguaging fell into three main categories: maintaining classroom culture, facilitating the academic task, and framing epistemic practices. Of the three categories of translanguaging, this paper focuses on how framing epistemic practices proved to be of paramount importance in the teacher presenting and supporting the suite of practices comprising scientific argumentation.