In this article, I study the "Experimental Plan of Educational Spreading" designed by Chilean composer, director, and pedagogue, Jorge Pena Hen (1928-1973). This plan, undertaken between 1964 and 1973 in the Chilean city of La Serena, provided free instrumental training for boys, girls, and young school students from diverse socioeconomic backgrounds, who later became part of the first Children's Symphonic Orchestra in Latin America in December 1964. This article aims to identify the strengths and weaknesses of the Plan to determine what factors influenced its success. To do this, it reviews the historical context and analyzes archival documents from the Escuela Experimental de Musica de La Serena -former Regional Conservatory-, referring mainly to the background, guidelines, and reception of the Plan. These documents, taken from primary sources reviewed in depth, are intended to shed light on this project, emphasizing the internal perception of the operation and development of the Plan. Finally, it describes two achievement indicators that show the project's success, explaining why the historical and cultural conditions were suitable for its implementation and how the main characteristics of the Plan's design favored its effectiveness.