This study explored children, preschool, and family characteristics that contribute to individual differences in the developmental trajectories of social competence and internalizing and externalizing behavior. Teachers reported on personality and social adjustment of 304 children at ages 3, 4, 5, and 6 years. Predictors of social adjustment included: (1) children's gender and the ratings of extraversion, conscientiousness, disagreeableness, and neuroticism; (2) maternal and paternal education, and parent-reported parenting practices at the beginning of the study; and (3) the child's age of entry to preschool. Child social adjustment was most strongly predicted by teacher-rated child personality. The change in a child's rank-order position on social competence was related to the change in the rank-order position on extraversion; the change in internalizing behavior was related particularly to a change in neuroticism, and the change in externalizing behavior especially to a change in disagreeableness. Specific family variables and the child's age at the time of entry into preschool played a minor but statistically significant role. (Contains 3 tables, 1 figure, and 3 notes.)