The development of research traditions focusing on language-in-use in classrooms has a deep history that spans the last six decades. The roots of conceptual understandings and epistemological perspectives central to studying ways language operates (cf., Aschner, 1961) and functions (cf., Cazden, John, & Hymes, 1972; Green, 1983; Guthrie & Hall, 1983; Cazden, 1986, 2017) in classrooms provide guiding principles for conceptualising and studying how opportunities for learning are linguistically, culturally, socially and academically constructed by teachers with their students within classrooms and other educational settings. The principles of inquiry are presented that frame epistemological decisions for studying how language operates and functions in classrooms for both teachers and their socially, linguistically, culturally and academically diverse students.