To investigate the antecedents of children's trait- and state-level peer competence, this study used a random-intercepts model to separately explore the influences of early stable predictors (i.e. temperament and attachment) and dynamic environmental factors (i.e. family and school) on peer competence. The study sample included children in the first, third, and fifth grades from the NICHD SECCYD (N = 594; 49.3% boys; 85.7% White). The results showed that peer competence is a trait (stable) and a state (malleable). Temperament (low anger/frustration and high inhibitory control) and secure attachment relationships contributed to trait-level peer competence. High-quality maternal sensitivity throughout the school grade levels ([beta] = 0.10 - 0.13) and positive classroom climate in the first grade predicted the state-level peer competence ([beta] = 0.11). Overall, this study has delineated the predictors of children's peer competence by examining both stable, trait-level factors and more dynamic, state-level factors.