This study examined gender differences in the level and developmental course of relational aggression in middle childhood, as well as early predictors and outcomes of relational aggression, after controlling for concurrent physical aggression. Relational (RAgg) and Physical aggression (PAgg) scores for 558 boys and 545 girls at the ages of eight to 11 in the NICHD Study of Early Child Care and Youth Development (SECCYD) were created by combining the highest rating for each item across mother and teacher reports. Longitudinal analyses were conducted using latent curve models of RAgg with PAgg as a time-varying covariate, with all parameters allowed to vary by gender. Boys and girls had different growth parameters of RAgg. Girls' RAgg intercept was higher, and the slope was not different from zero; boys' RAgg intercept was lower, and the slope declined. Mother-child conflict in early childhood predicted RAgg intercept for both boys and girls, but maternal harsh control and sensitivity were also uniquely predictive for girls whereas center care was uniquely predictive for boys. RAgg intercept predicted adolescent self-reports of depression for girls and delinquency and risk-taking for both boys and girls; the magnitude of the association with risk taking was significantly greater for boys.