This paper critically examines evaluations of the effects of early childhood development programs in Third World countries. Introductory comments underscoring the importance of preschool interventions for the improvement of primary schools are followed by a section explaining the paper's analytical framework, which posits an interactive relationship between the readiness of children for school and the readiness of schools for children. The readiness of children for school is defined in terms of children's physical capabilities and activity levels, cognitive ability, learning style, knowledge base, and social and psychological competencies, while the readiness of schools for children is considered in terms of availability, accessibility, quality, and adaptation to local needs and circumstances. This section concludes by examining the influence of these factors on school enrollment, progress, and performance. The second section reviews studies of: (1) nutrition intervention programs in Guatemala; Cali and Bogota, Colombia; and Pueblo, Mexico; (2) early childhood education programs in Asia, Latin America, and the Middle East; and (3) the effects of early intervention programs on enrollment, promotion, grade repetition, dropout rates, and performance. The following sections review the Indian Integrated Child Development Services and Peru's Programas No-Formal de Educacion Inicial. In the final section, the implications of these findings are discussed and policy recommendations regarding program integration, organization, and evaluation are presented. (AC)