Sex is one of the most robust predictors of self-control, with a consistent finding that girls score higher on a variety of measures of self-control. In this research, the authors investigate three possible reasons for why this is true: first, they examine whether current predictors of self-control mediate the effect of sex on self-control, second, they examine whether sex moderates the effect of current predictors on self-control and third, they examine the possibility that the causes of self-control are gendered, necessitating different causal models for boys and girls. Using data from the Children of the National Longitudinal Survey of Youth79, the authors assess three, related questions: Is the sex effect on self-control mediated by current predictors of self-control? Does sex moderate the effects of current predictors of self-control? Does the causal model predicting self-control differ for boys and girls? The authors found that the sex effect on self-control is robust: does not moderate the etiology of self-control; and although partially mediated by etiological variables, remains a significant predictor of self-control. The authors also found that current predictors do a poor job of explaining girls' acquisition of self-control, suggesting a gendered etiology of self-control. (Published Abstract) Tables, appendixes, notes, and references