The experience of the 1st year of the Nicaragua Radio Mathematics Project suggests the following general conclusions about the design and use of radio lessons: children are most attentive to radio lessons when they are responding actively; mathematical activities are more engaging than stories for 1st grade children; children listen to instructions and in most cases repetition is unnecessary; children can learn new topics from the radio lessons; and teachers are able to incorporate radio lessons into their daily routine. The Nicaragua Radio Mathematics Project was initiated in 1973 to develop and test a mathematics curriculum dependent upon radio presentations and using teacher-directed activities as a supplement to the radio lessons. The research activities of the project were related closely to the phases of lesson development: in Phase A the research was formative and directed toward lesson improvement as well as limited to a small number of classrooms; and in Phase B the number of classrooms was expanded and a control group was included changing the emphasis to one of comparative assessment of achievement levels between the experimental and control groups. The Radio Mathematics Project may account for all of the mathematics instruction children receive. A daily lesson consists of a 20-minute radio presentation followed by about 20 minutes of teacher-directed activities. No textbooks are used. Printed material is limited to a 1-page worksheet for each child each day. Project lessons are based on the mathematics curriculum specified by the Nicaraguan Ministry of Education. The process of designing radio lessons from the rather general specifications of the Ministry of Education curriculum guide involves several steps and these are outlined. During 1975 the project produced 150 first-grade mathematics lessons that were presented daily in 16 classrooms in the Department of Masaya and in an additional 6 classrooms in the Department of Granada. In general the children responded well to the fast pace of the lessons and participated actively. The childrens response to the entertainment portions of the lessons replicated earlier findings i.e. the most successful activities were songs and physical games and the least successful were stories. The children preferred the mathematical portions of the lessons to the stories.