This paper summarizes current knowledge from research on teacher effectiveness and discusses the relationship between those findings and educational policy. Few teaching strategies have been studied in different types of environments, so validated knowledge on teacher effectiveness exists for only a few issues. Research findings discussed include: the amount of learning by pupils is related to exposure to content; teachers maximizing pupil learning allocate more classroom time to academic activities; learning is maximized when pupils move briskly through curriculum and experience consistent success; learning is greater where pupils are taught and supervised by teachers rather than working on their own; greater learning is associated with frequent presentation of materials and practice and application of what is learned; pupil morale and achievement are higher in relaxed, supportive classrooms; and teacher beliefs about students correlate with pupil achievement. The relationship between research on teaching and policy is complex and indirect--the authors define the differences between the cultures of research and policymaking and stress the importance of including teacher effectiveness research findings and concepts in teacher training. They discuss the value of self-study for teachers, the problems of teacher evaluation and merit pay, and areas needing future research, and conclude with a discussion on innovations and improvement. (MD)