Fourteen classrooms were grouped according to environmental format (open/mixed/traditional) and differences in teacher-student interaction patterns and perceptions of responsibility for outcomes assessed. As predicted, open classrooms showed the highest percentage of dyadic interactions. Also as predicted, open classrooms tended to show the lowest percentage of group interactions, highest percentage of interactions concerned with a student's individual work, and lowest percentage concerned with answering specific academic questions. Contrary to prediction, teachers of traditional classrooms rated students more personally responsible for failure than open classroom teachers. Finally, students in more open classrooms tended to perceive themselves as more responsible for success than students in traditional classrooms. Results are discussed in light of the philosophical bases which lead to the adoption of the open classroom format. (Author)