This paper assumes that environmental inadequacy is the primary factor leading to progressive intellectual retardation and inability to cope in a complex society. An intervention project begun in 1966 was designed to develop cognitive, motivational, personal style, and physical variables, which are functional categories related to competence. Subjects included 60 disadvantaged preschoolers (the "target" children), their younger siblings (the experimental groups), and their mothers. Group I (the maximum impact group) involved the mother and the target child at the Early Training Center. The mother's sequential program consisted of skill development, observation, and participation as a teacher. Aptitudes of skills for environmental mastery and sustaining attitudes for continued growth were developed in target children. In Group II, the target child was the only member of the family enrolled in the program. Families in Group III (the home visitor group) had no contact with the center, but a home-visiting teacher described procedures. A natural environmental group was chosen to match demographic characteristics of treatment families. In 2 1/2 years, younger siblings whose mothers participated were superior in all comparisons. Analysis of psychometric data on target children was significantly greater than those where no parental contact was maintained. (DO)