In 1921, Harlow Shapley became the director of the Harvard College Observatory to replace the deceased Edward Charles Pickering. Under his leadership, it became one of the world's most important centers for astronomy training and research. Shapley established the graduate school of astronomy as part of the educational structure of Harvard University. He was also responsible for mandating that public education be made a part of the Observatory's mission; a requirement for students in the Harvard program was lectures and presentations for school children. Shapley remained as the Observatory's director until 1952, and then continued research as the Paine Professor of Practical Astronomy until his retirement in 1956. After that, he continued his work as both a lecturer and an author.