The preschool programs developed for disadvantaged children in the 1960s and 1970s not only built on this new work but also incorporated views of theory and practice from a wide variety of traditions in psychology and education. Despite the programs’ emphasis on their potential cognitive benefits, most sought to enhance the development and well-being of the whole child (Day and Parker, 1977). Especially in the early years, they had to address concerns that preschool programs might negatively affect social and emotional development by separating children from their mothers (Caldwell and Smith, 1968). Researchers developed “model” programs specifically to investigate the potential for preschool education to influence the learning and development of economically disadvantaged children. Much of what is known about the nature and magnitude of preschool education’s influences derives from rigorous studies of these model programs. Such studies also provide considerable information about the characteristics of highly effective programs.