Several assessment tools have been developed to assess psychopathic traits in childhood and adolescence. However, knowledge on the continuity and change in psychopathic traits remains limited, especially because of uncertainties regarding the capacity of these tools to assess these traits using a common metric across development. To fill this void, this study tested the measurement invariance of the Child Problematic Traits Inventory (CPTI), a teacher-rated scale designed to assess psychopathic traits from ages 3 to 12 years. Data were drawn from a Swedish population-based sample of 2,121 children followed longitudinally across 8 years from early to late childhood. Results from confirmatory factor analyses and multigroup invariance analyses showed an excellent fit of the theoretically proposed three-factor model of the CPTI and supported the scalar invariance hypothesis of this model across sexes at all assessment time points. Longitudinal invariance analyses further supported the hypothesis of scalar invariance of the three-factor model across the study design, hence suggesting that dimension scores can be reliably compared across this period. These results substantially add to previous psychometric evaluations of the CPTI by suggesting that assessments of psychopathic traits using the CPTI confer a metric that is comparable both across sexes and from early childhood to late childhood. Implications for future longitudinal studies aimed at understanding the developmental origins of these traits are discussed.