The purpose of this study was to determine whether a behavioral rating measure of low self-control and an attitudinal measure of low self-control can be viewed as measuring the same construct. It was hypothesized that the externalizing scale of the Behavior Problems Index (BPI-Ext), which served as a behavioral rating measure of low self-control in the current study, would display greater similarity to a 6-item self-report of antisocial, but not necessarily delinquent, behavior (SR-AB) measure than it would a 6-item attitudinal self-report measure of low self-control, labeled the reactive criminal thinking (SR-RCT) scale. This study was conducted on a sample of 6280 children (3144 boys, 3136 girls) from the National Longitudinal Survey of Youth-Child (NLSY-C). A pair of confirmatory factor analyses revealed that the BPI-Ext and SR-RCT scales appeared to form two distinct constructs. In addition, the BPI-Ext correlated significantly better with the SR-AB than with the SR-RCT and the BPI-Ext and SR-AB achieved moderate negative correlations with measures of attention, concentration, achievement, and general aptitude, whereas the SR-RCT achieved small positive correlations. These results indicate that behavioral and attitudinal measures of low self-control are measuring different constructs, the former impulsive behavior and the latter reactive criminal thinking.