This syudy was designed to investigate the effectiveness of an all-day kindergarten program based upon the interactionism model, which was implemented in Duksung Women's University Kindergarten during the 1990 school year, with a sample of 18 children(10 4-year-olds and 8 5-year-olds ; 11 boys and 7 girls) and their parents. To assess its outcomes, the children's heights and weights, and three different standardized test scores, i.e., social adjustment, IQ, and academic achievement tests, were examined. To compare all-day and half-day kindergarten programs, a nonequivalent control group was formed through matching on the basis of pretest IQ. To ascertain the effectiveness of the program from the parents' perspective, the in-depth interviews with parents were conducted and analyzed. Comparison of the all-day and half-day groups showed both programs were effective in improving kindergarteners' physical, cognitive, and social development and academic achievent. The results also suggested that the effects of the length of the kindergarten program on the child's growth and development were the same for all the age levels and for both boys and girls. Furthermore, it was revealed that the parents were satisfied with the program, and they also felt the curriculum model valuable. In conclusion, all day kindergarten program met the social and educational needs of both children and parents. Some recommendations were presented in terms of curriculum improvement and evaluation.