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The influence of Tourette syndrome and chronic tic disorders on academic performance has not been objectively quantified.To investigate the association of Tourette syndrome and chronic tic disorders with objectively measured educational outcomes, adjusting for measured covariates and unmeasured factors shared between siblings and taking common psychiatric comorbidities into account.A population-based birth cohort consisting of all individuals born in Sweden from 1976 to 1998 was followed up until December 2013. Individuals with organic brain disorders, mental retardation, and 2 foreign-born parents were excluded. We further identified families with at least 2 singleton full siblings and families with siblings discordant for Tourette syndrome or chronic tic disorders.Previously validated International Classification of Diseases diagnoses of Tourette syndrome or chronic tic disorders in the Swedish National Patient Register.Eligibility to access upper secondary school after compulsory education, finishing upper secondary school, starting a university degree, and finishing a university degree.Of the 2 115 554 individuals in the cohort, 3590 had registered a diagnosis of Tourette syndrome or a chronic tic disorder in specialist care (of whom 2822 [78.6%] were male; median [interquartile] age at first diagnosis, 14.0 [11-18] years). Of 726 198 families with at least 2 singleton full siblings, 2697 included siblings discordant for these disorders. Compared with unexposed individuals, people with Tourette syndrome or chronic tic disorders were significantly less likely to pass all core and additional courses at the end of compulsory school (odds ratios ranging from 0.23 [95% CI, 0.20-0.26] for the handcraft textile/wood course to 0.36 [95% CI, 0.31-0.41] for the English language course) and to access a vocational program (adjusted OR [aOR], 0.31; 95% CI, 0.28-0.34) or academic program (aOR, 0.43; 95% CI, 0.39-0.47) in upper secondary education. Individuals with the disorders were also less likely to finish upper secondary education (aOR, 0.35; 95% CI, 0.32-0.37), start a university degree (aOR, 0.41; 95% CI, 0.37-0.46), and finish a university degree (aOR, 0.39; 95% CI, 0.32-0.48). The results were only marginally attenuated in the fully adjusted sibling comparison models. Exclusion of patients with neuropsychiatric comorbidities, particularly attention-deficit/hyperactivity disorder and pervasive developmental disorders, resulted in attenuated estimates, but patients with Tourette syndrome or chronic tic disorders were still significantly impaired across all outcomes.Help-seeking individuals with Tourette syndrome or chronic tic disorders seen in specialist settings experience substantial academic underachievement across all educational levels, spanning from compulsory school to university, even after accounting for multiple confounding factors and psychiatric comorbidities.