A conceptual and empirical analysis of findings from the development of a comprehensive classroom-based, direct observational measure of classroom environment is presented in this paper. The System for Teaching and Learning Assessment and Review (STAR) differs from traditional instruments of direct, systematic classroom observation in that it assesses elements of both teaching and learning. Observation is based on four performance dimensions: preparation, planning, and evaluation; classroom and behavior management; learning environment; and enhancement of student learning. Findings demonstrate the usefulness of the instrument as a comprehensive measure of the total learning environment, applicable to the concept of learning environments as highly interactive, complex social systems in which both teachers and students actively participate in learning. The use of multimethod approaches to understand the complexities of classroom learning environments from multiple viewpoints is recommended. Appendices summarize the four performance dimensions and components of the psychosocial and physical learning environments. (42 references) (LMI)