Refugee children in the Nordic countries have been reported to perform poorly in school and carry a high burden of familial posttraumatic stress. The present study aimed to investigate the impact of maternal and paternal posttraumatic stress on the school performance of refugee children. We used national register data on school grades at age 15-16 along with demographic and migration indicators during 2011-2017 in a population of 18,831 children in refugee families in Stockholm County, Sweden. Parental posttraumatic stress was identified in regional data from three levels of care, including a tertiary treatment center for victims of torture and war. Multivariable linear and logistic regression models were fitted to analyze (a) mean grade point averages as Z scores and (b) eligibility for upper secondary school. In fully adjusted models, children exposed to paternal posttraumatic stress had a lower mean grade point average, SD = -0.14, 95% CI [-0.22, -0.07], and higher odds of not being eligible for upper secondary education, OR = 1.37, 95% CI [1.14, 1.65]. Maternal posttraumatic stress had a similar crude effect on school performance, SD = -0.15, 95% CI [-0.22, -0.07], OR = 1.25, 95% CI [1.00, 1.55], which was attenuated after adjusting for single-parent households and the use of child psychiatric services. The effects were similar for boys and girls as well as for different levels of care. Parental posttraumatic stress had a small negative effect on school performance in refugee children, adding to the intergenerational consequences of psychological trauma.