This paper reviews the findings of research on the teaching effectiveness of both instructional and open broadcast television since 1968, pointing out that the presence of a mentor who shares in the viewing and discusses what is seen with the child is a critical factor in what a child will learn. Discussion is divided into research prior to 1975; recent research thrusts; characteristics of effective instructional television programs, viewing, and planning for teaching; the research production (formative evaluation) approach; related research into teaching design; research on the effects of commercial television; and the implications of research findings for teachers. Seven case studies are presented in chart form from a series of 15 examining the cognitive and attitudinal effects on students and teachers of using the Trade-offs instructional television series to teach economics in grades five and six. A bibliography of 37 items is divided into research prior to 1975, recent research thrusts, the Research Production Approach, and related research into teaching design. (CHC)