This report briefly describes the procedures for assessing children's psychological development and the data analytic framework used in the New York City Infant Day Care Study. This study is a 5-year, longitudinal investigation in which infants in group and family day care programs and infants reared at home are compared. Children in the study are assessed on various aspects of psychological development (cognitive, language, social, personality, and emotional), at 6, 12, 18, and 36 months of age. The first psychological evaluation of the children serves as a baseline measure of their psychological functioning. Subsequent assessments are considered outcome measures reflecting the programs' effects. The sequence and nature of tests and interviews used in this aspect of the study are reported and related to the other areas of the study. The report concludes with a discussion of the rationale and design of the data analytic framework used in comparing: (1) initial and demographic characteristics of children and families in group and family day care, (2) infant day care environments, and (3) developmental outcomes. (ED)