Aims The objective of the study was to compare grade point averages (GPAs) on compulsory school exit exams (exam GPA) and educational attainment at age 16 and 20 for individuals with and without type 1 diabetes. Methods This study was a population-based retrospective cohort study, which included the 1991 to 1998 birth cohorts in Denmark. Follow-up was conducted at age 16 and 20 (follow-up period; 1 January, 2007 to 31 December, 2018). There were 2083 individuals with and 555,929 individuals without type 1 diabetes. Linear regression and generalized linear models compared outcomes with and without adjustments for socio-economic characteristics. Results A total of 558,012 individuals (51% males) were followed to the age of 20. Having type 1 diabetes was associated with a lower exam GPA when adjusting for socio-economic status (difference: -0.05 (95% CI, -0.09 to -0.01), a higher relative risk of not completing compulsory school by age 16 (1.37, 95% CI, 1.22 to 1.53)), and a higher relative risk of not completing or being enrolled in upper secondary education by age 20 (1.05, 95% CI, 1.00 to 1.10). Haemoglobin A1c (HbA1c) 7 BGM/day and insulin pump use were associated with better educational achievement. Conclusion Type 1 diabetes was associated with a marginally lower exam GPA and a higher risk of not completing compulsory school by age 16 and lower educational attainment by age 20. The findings were modified by HbA1c, BGM and insulin pump use.