This paper summarizes research conducted to assess how and to what extent teachers actively use and manipulate the physical classroom learning environment as part of their instructional design. A structured interview and participant observation were used to gather data from several teachers at all grade levels, including national board certified teachers. Preliminary findings include the design principles used by various teachers, which indicate that rather than receiving education on research-based design principles during their formal education, teachers have relied on trial-and-error methods. (Contains 19 references.) (EV)