The idea of childhood as a social invention, in retrospect, is hardly credible. In the Bible, in writings of the Greeks and Romans, and in the works of the first great educator of the modern era, Comenius, children were recognized as being both different from adults and different from one another with respect to their stages of development. To be sure, the scientific study of children and the increased length of life in modern times have enhanced our understanding of age differences, but they have always been acknowledged.