Building on previous studies of ESL and content teachers' collaboration, this qualitative case study relied on Davies and Harré's positioning theory as a theoretical lens to examine the influences that collaboration between an ESL teacher and a language arts teacher had on the language arts teacher's approach to planning for and teaching ESL students. Data collection included three audio recorded semi-structured interviews, two video recorded collaborative planning sessions, two reflective journals written by the language arts teacher, document analysis of the created lesson plan documents, and field notes. The findings showed that the language arts teacher changed her perceptions about the content teacher's role, lesson plan design, and her views about ESL students while working in collaboration with an ESL teacher. These findings implicate the potential for ESL and content teachers' collaboration to be a space to challenge the content teachers' accepted notions about language instruction for ESL students and highlight the ESL teacher's strengthened role in the collaborative partnership. Further, this study warrants further exploration into ESL and content teachers' collaboration in middle school content classrooms.