Research on the utilization of educational media, or electronic classroom instructional aids, in primary schools in developing countries is reviewed in this paper. Five kinds of hardware--radio, television, computers, videodiscs, and hand-held electronic devices--are compared according to cost and learning effectiveness. A model of learning production is used to define the educational system in terms of its interaction with family and society, and to illustrate the relationships among the components of educational management, which include content, instructional materials, classroom management, physical facilities, and learning technology. Radio was found to be the most cost effective means of improving both scope and quality of instruction. Effectiveness is enhanced if the technologies are used in combination with curriculum development, instructional resources, administrator support, and teacher training. A comparative table, describing seven educational interventions, a diagram of learning production, and an extensive bibliography are included. (LMI)