This paper presents a developmental study of the problem solving strategies of reflective and impulsive children. Subjects for the study were 30 nine-year-olds, 39 eleven-year-olds, and 23 thirteen-year-olds who had been classified as reflective or impulsive at ages 7, 9, and 11 and who had been followed longitudinally over a three year period. The Matching Familiar Figures (MFF) test and four problem solving tasks which provided information on problem solving strategies were administered each year during the program. The results of the study suggest that children who were classified as reflective on the MFF were more likely to adopt more systematic and/or mature strategies on tasks which required sequential hypothesis testing and information processing than were impulsive children of the same age. The longitudinal analysis suggested that reflective children acquired efficient strategies more rapidly over the early elementary years than did impulsive children. At the same time, the relative impact of reflection-impulsivity varied systematically with the developmental level of the subjects, with the relative difficulty of the problem for children at different stages of cognitive development, and with repeated experiences with the problems used in the study. (BD)