Abstract: The purpose of the present study was to examine the relations among elementary school children's effortful control, peer interactions and school adjustment. Data were gathered on 344 ethnically diverse children (M age at Time 1 = 7.5yrs; N = 171 girls; 173 boys) attending four predominantly low- to middle-class schools in the southwestern United States. Participating children as well as their parents, teachers and peers provided questionnaire and peer sociometric data at two time points. Data were collected in 1st and 3rd grades (T1) and one year later (namely, 2nd and 4th grades, respectively; T2). Three main research questions were addressed: (1) whether there were direct relations among children's effortful control, peer interactions and school adjustment; (2) whether peer interactions mediated the relation between children's effortful control and school adjustment; and (3) whether bidirectional relations existed between children's effortful control, peer interactions and school adjustment. Structural equation modeling was used to analyze the data and examine direct, mediational and bi-directional relations among the study constructs. In general, correlational analyses indicated support for within and across time relations among children's effortful control, peer interactions and school adjustment as hypothesized. Results from models within T1 and T2, were consistent with the prediction that the relations between effortful control and school adjustment would be mediated by children's peer interactions. Also as expected, children's effortful control was negatively related with peer victimization and lower levels of peer acceptance. Additionally, peer victimization and lower levels of acceptance were negatively related to children's school adjustment. Finally, although the longitudinal model supported neither the hypothesis that peer interactions would mediate the relation between children's effortful control and school adjustment across time, nor the existence of bidirectional relations among constructs, correlations did indicate that these relations may exist. Possible explanations for these findings and implications for future research were also discussed.