The Radio Mathematics Project was established to design, implement, and evaluate a prototype system of teaching elementary mathematics using radio as the major medium of instruction. Daily mathematics lessons were presented to first and second graders in rural and urban primary schools in Nicaragua. Lessons had a radio and a postbroadcast portion, each about 30 minutes long. Radio lessons were constructed from segments of instructional material and entertainment activities, both of which required a high level of active response from the children. It was found that first grade children learned new mathematical concepts and skills from radio instruction supplemented by a student worksheet. Children remained attentive and responsive for the radio lesson, provided they had the opportunity to respond frequently. Children were able to respond at the rate of three to four times a minute. They enjoyed the instructional segments of the lessons, and the entertainment segments were not necessary to maintain the children's attention. Test results indicated that children in radio classrooms performed better than children in traditional classrooms on all topics taught by radio. (Author/CH)