The current investigation tested childhood developmental antecedents of adolescent empathy, self-control, callous-unemotionality, and delinquency, namely difficult temperament, positive socialization experiences, and intelligence; it also tested potential mediation effects of temperament via socialization. Data were collected as part of the National Institute of Child Health and Human Development Early Child Care and Youth Development Study, which followed N = 1364 children from birth through 15 years (51% female, 80% European American). Early positive socialization (maternal sensitivity, secure attachment, and quality home environment) and temperament variables were assessed from 1 to 36 months, intelligence at age 9, and self-control, empathy, callous-unemotionality, and delinquency at age 15. Based on structural equation modeling hypothesis tests, early positive socialization positively predicted self-control and empathy, and negatively predicted callous-unemotionality and delinquency. Intelligence uniquely and positively predicted empathy. Difficult infant temperament indirectly predicted each of the four traits through early positive socialization. Important research and practical implications are discussed.