Abstract
Attention-deficit hyperactivity disorder (ADHD) is prevalent in children and associated with lower education performance. This association is often obtained from observational studies, which have limited ability to identify causal relationships. Knowledge of causes is useful, because it delineates intervention avenues more clearly, but research into causation in childhood is hindered by ethical and practical limitations to randomized clinical trials. The present study uses twin study designs and polygenic risk scores (PRS) to investigate the causal relationship between ADHD symptoms and poor educational performance. We combined family-based direction of causation modeling and Mendelian randomization (MR) approaches and applied them to ABCD study data for improved causal inference. The models used necessarily make assumptions about either horizontal pleiotropy, or the level of individual-specific confounding factors. Results support the hypothesis that ADHD symptoms have a causal effect on educational performance, and vice versa. No heterogeneity related to sex was found, nor moderation of causal estimates by gender. These findings highlight the complex interplay between ADHD and educational outcomes and emphasize the need for larger sample sizes in future research.