A study examined the language and interactions that occurred in classes where teachers felt they were providing an environment that fostered reasoning about their coursework. The discourse within the diverse classrooms of eight high school teachers (two each in American literature, American history, biology, and physics) was examined. In each discipline, the teachers' instructional styles differed, with one placing more emphasis on the content and the other on the students' ways of thinking about that content. Results indicated that: (1) reasoning was taught and learned in academic classes; (2) such reasoning was subject-specific and embedded in the pragmatic routines of subject-driven lessons; (3) the specifications of such reasoning were implicit and therefore unavailable for overt use in lesson planning or as strategic knowledge to be taught; (4) this kind of discipline-specific reasoning may or may not be sufficient for successful participation in disciplinary learning; and (5) certain types of pedagogical approaches or styles may inhibit or support such discipline-appropriate thinking. Findings suggest the need for additional studies involving more teachers before explicit suggestions for the recasting of instruction along discipline-specific lines can be made. The categories identified may provide a useful place to start an investigation leading toward productive instructional reform. (Two tables of data are included; 39 references are attached.) (RS)