On 17 April 1975, the communist Khmer Rouge marched into Phnom Penh and established Democratic Kampuchea. Declaring an end to “over two thousand years of Cambodian history,” Khmer Rouge leader Pol Pot announced a new beginning, referred to metaphorically by scholars of the period as the “Year Zero.” The “new Cambodia” lasted exactly three years, eight months, and twenty days, during which time the people of Cambodia were subjected to a cataclysmic social experiment as part of what one historian has termed “the world's most radical … revolution.”

In recent years social scientists have devoted increasing attention to the question of how members of ethnic and racial minorities are affected by living in segregated neighborhoods. A central concern has been that the poverty of these neighborhoods may be self-perpetuating. One obvious possibility is that this could be caused by reducing human capital formation: children in ghettos might be less likely than their counterparts elsewhere to attend school, perhaps because their demand for education is lower, or because their access to schools is restricted, or as a result of a combination of the two.

One of the quiet cultural transformations of the twentieth century in the United States has been the widespread consensus over the meaningfulness of age gradations among children and youths. Joseph Kett's important book on the history of the idea of adolescence examined the first significant triumph of experts in promoting the concept of human development in American institutional life. Who could have predicted at the dawn of the twentieth century the swift success of the “adolescent idea” and the subdivision of stages in growing up that has occurred since? Certainly the rise of the expert and the medicalization of “deviance” have contributed significantly to the broad acceptance of age gradations and the developmental perspective. But schooling, the most pervasive of all modern institutions has had the greatest influence on the willingness of Americans to think through novel categories of cognitive, emotional, and physiological growth and well-being in young people. While the passage and enforcement of compulsory schooling and a concomitant need to make distinctions among children's school performance (which led to age-grading) established the framework for thinking about pupils developmentally, it was the voluntary extension of schooling that proved the true measure of parents' willing adoption of the developmental view. The critical period of growth in schooling beyond the minimum required by law occurred between 1910 and 1940, when high school attendance grew dramatically. One factor in its expansion was the invention of the high school “drop out,” which both constituted and reflected the spread of the idea that high school was within the reach of every girl and boy and that every child, moreover, should want to attend high school.