Meta-analyses have demonstrated that other-ratings of Conscientiousness are stronger predictors of academic achievement than are self-ratings. The current study (N = 410 high school students) examined whether this effect applies for all facets of Conscientiousness. Compared to self-reports, parent-reports showed stronger prediction of GPA and of other school life variables such as disciplinary infractions and involvement in school clubs. The difference between parent- and self-reports was stronger for outcome-linked facets such as Industriousness than for process-linked facets such as Tidiness. We suggest that this difference is due to the different types of information used by the self as compared to observers when rating personality items. Our results help to explain the reporting biases evident in self- and parent-ratings, have implications for the appropriateness of self- and parent-report personality protocols in applied settings (e.g., training, selection), and should provide guidance for educational interventions focused upon goals, habits and motivations.