This is a partial report of a longitudinal investigation designed to assess the psychological effects of an experimentally conducted day care program on children during the first 30 months of life. The experimental subjects were Chinese and Caucasian children from working and middle class families who were cared for at a special group care center five days a week from 3 1/2 to 30 months of age. The major control group consisted of children reared totally at home but matched with the experimental children on ethnicity, social class and sex. The children were assessed at 3 1/2, 5 1/2, 7 1/2, 9 1/2, 11 1/2, 13 1/2, 20 and 29 months, although this paper deals only with some of the data gathered during the assessments at 20 and 29 months. The three assessments during the second year evaluated patterns of play with objects, social behavior with peers, attachment behavior to the mother and surrogate caretaker, as well as cognitive competences. The data revealed little difference between the day care and home control children with respect to cognitive functioning, language, attachment, separation protest, and tempo of play. The only simple effect of form of rearing involved behavior with unfamiliar peers. The day care children were less vigilant and less inhibited in the presence of unfamiliar children than were those reared at home. It was concluded that the home environment influenced children's early development more than experiences in the day care context. (Author/BRT)