AbstractObjectiveThis study investigated the associations between personality traits at age 8 and academic performance between ages 10 and 14, controlling for family confounds.BackgroundMany studies have shown links between children’s personality traits and their school performance. However, we lack evidence on whether these associations remain after genetic and environmental confounders are accounted for.MethodSibling data from the Norwegian Mother and Child Cohort Study (MoBa) were used (n = 9701). First, we estimated the overall associations between Big Five personality traits and academic performance, including literacy, numeracy, and foreign language. Second, we added sibling fixed effects to remove unmeasured confounders shared by siblings as well as rating bias.ResultsOpenness to Experience (between‐person β = 0.22 [95% CI: 0.21–0.24]) and Conscientiousness (between‐person β = 0.18 [95% CI 0.16–0.20]) were most strongly related to educational performance. Agreeableness (between‐person β = 0.06 [95% CI −0.08–0.04]) and Extraversion (between‐person β = 0.02 [95% CI 0.00–0.04]) showed small associations with educational performance. Neuroticism had a moderate negative association (between‐person β = −0.14 [95% CI −0.15–0.11]). All associations between personality and performance were robust to confounding: the within‐family estimates from sibling fixed‐effects models overlapped with the between‐person effects. Finally, childhood personality was equally predictive of educational performance across ages and genders.ConclusionsAlthough family background is influential for academic achievement, it does not confound associations with personality. Childhood personality traits reflect unbiased and consistent individual differences in educational potential.