The study assessed the development over a 3-year period of children's ability to differentiate accurately peers' physical, behavioral, and psychological characteristics. Participants were 4 girls and 10 boys (averaging 95.05 months of age at the beginning of the study), first seen when they were in second grade and retested as third and fourth graders. Children were presented with pictures of all possible pair of classmates and were asked to make judgments on their peers' height, tendency to get angry, mathematical and running abilities, and to indicate their liking for classmates. Objective measures of each characteristic were also obtained. Children's differentiating ability and the accuracy of their judgments increased over time. In second grade, only few characteristics were differentiated, all in relation to height; and judgments in general were inaccurate. In third grade, differentiation increased, and children were accurate at judging peers' height. By fourth grade, children differentiated between most characteristics and were accurate at judging height and running speed. Three individual patterns of development at differentiating accurately peers' characteristics were identified, but most children matched the group's normative developmental pattern. Two procedures for analyzing group paired-comparison data were contrasted