This paper describes a case study of how a middle school literacy coach and a science teacher attempted to improve disciplinary literacy teaching in a sixth-grade science class. The collaborative inquiry exposed the disciplinary knowledge gap of the literacy coach (a former language arts teacher) and the science teacher's limited knowledge of literacy instruction. These shared disciplinary knowledge gaps necessitated the co-construction of collaborative practices to ameliorate the tension and improve disciplinary literacy instruction. Through a recognition of individual knowledge and the use of responsive disciplinary teaching, the participants created collaborative symbiosis. To improve disciplinary literacy teaching, schools should recognize teacher disciplinary knowledge and expand participation in discipline-specific collaborative inquiry.