Background/Context: Most people who study the history and philosophy of education have heard of essentialism, but few people know the story behind how, when, and why the movement came to exist. This paper tells this story for the first time. Purpose/Conclusions: This essay has three purposes. First, it provides an introduction to the life and career of William Chandler Bagley, a prominent professor of education at Teachers College, Columbia University, from 1917 until his retirement in 1939. Following an introduction to Bagley's life, this work describes the founding of essentialism by drawing upon numerous primary and secondary sources to place this movement within the social and historical context in which it developed. The author pays careful attention to the story of how and why the founding of essentialism took place on the same day that John Dewey delivered his "Experience and Education" lecture at the 12th biennial convocation of Kappa Delta Pi. The paper then argues that what came to be known as essentialism represents a forgotten tradition in American educational history, one that is much richer than contemporary calls for "standards and accountability," which grew out of the economically driven "A Nation at Risk" report of 1983. To conclude, the essay calls for more substantive attention to liberal education, purpose, moral philosophy, and curriculum for teaching teachers, all of which were at the heart of essentialist educational thought, but are now forgotten in an age obsessed with economic efficiency. The author calls upon contemporary leaders in American education to reconsider essentialism as a powerful philosophy that has great potential for the future of the teaching profession. Research Design: This paper is written from the perspective of history and is based upon the long-established methodology from the field of historiography.