Objectives Childhood cataract is a chronic condition that may interfere with the child's learning capacities. We aimed to investigate whether childhood cataract influences academic development by comparing school performance in reading and mathematics in children with cataract to a matched control group. Design Nationwide registry-based cohort study. Settings Two surgical centres that perform all treatments for childhood cataract in Denmark. Participants Children born between 2000 and 2009 diagnosed with cataract before 10 years of age (n=275) and an age-matched and sex-matched control group (n=2473). Main outcome measures School performance was assessed as test scores in national tests performed at regular intervals from grade 2 to grade 8 in reading and mathematics. Analyses were corrected for birth origin, child somatic and mental disorder and parental socioeconomic status and mental disorders. Results Of 275 children, 85 (30.9%) were operated for bilateral cataract, 79 (28.7%) unilateral cataract and 111 (40,4%) were not operated. We found that children with cataract have lower participation rate in the tests (62.5%) compared with the control cohort (77.2%) (p value=0.0001). After adjusting the pooled analyses for birth origin, somatic and mental disease in the child and parental socioeconomic status and mental disorders, we found that the children with cataract scored significantly lower in mathematics compared with those without cataract (mean difference=-4.78, 95% CI: -8.18 to -1.38, p value=0.006), whereas no difference was found regarding scores in reading (p=0.576). The lower score in mathematics was driven by children who had been operated for bilateral cataract (p-value=0.004). Conclusion Children with cataract without somatic or neurodevelopmental comorbidities or psychosocial adversities seem to do well in school, whereas children operated for bilateral cataract have higher frequencies of difficulties in mathematical tasks.