Drawing on a sample of twin children from the Early Childhood Longitudinal Study, Birth Cohort (ECLS-B; Snow et al., 2009), the current study analyzed 2 of the most prominent predictors of externalizing behavioral problems (EBP) in children: (a) parental use of spankings and (b) childhood self-regulation. A variety of statistical techniques were employed, and, overall, the findings can be summarized into 2 points. First, the results show that the relationships among spanking, self-regulation, and EBP are highly nuanced in that multiple explanations for their intercorrelations appear to fit the data (e.g., bidirectional relationships and shared methods variance). Second, genetic influences accounted for variance in each variable (EBP, spankings received, self-regulation) and even explained a portion of the covariance among the different variables. Thus, research that does not consider genetic influences when analyzing these associations runs a risk of model misspecification.