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ADHD and Student Grades in Children from the ABCD Study®: A Twin and Siblings Study

Luís Fernando Silva Castro-de-Araujo, Daniel Zhou, Mei‐Hsin Su, Sydney Kramer, Robert J. Loughnan, Michael C. Neale · 2026 · 2 citationsRead the paper

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.

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Shown in the lab

ADHD symptoms have a significant causal effect on educational performance. — -0.31 [95% CI: -0.62, -0.11] (unstandardized estimate) (MR-DoC2 model applied to European ancestry subsample)
Educational performance does not have a significant causal effect on ADHD symptoms. — -0.60 [95% CI: -1.2, 0.03] (unstandardized estimate) (MR-DoC2 model applied to European ancestry subsample)
No evidence of sex limitation or moderation of causal estimates by gender. (Likelihood ratio tests comparing scalar and equated A/C models)
ADHD symptoms are best fit by an AE model, while school grades are best fit by an ACE model. — ADHD: A=0.59, E=0.41; Grades: A=0.42, C=0.43, E=0.15 (Bivariate ACE reduction)

Setup: 1,523 complete pairs of twins and siblings from the ABCD Study (follow-up year 3); MR analyses restricted to a European ancestry subsample (n=1,071).
How: The study used family-based direction of causation (DoC) modeling and Mendelian randomization (MR-DoC, MR-DoC2) extensions of the twin design. It incorporated polygenic risk scores (PRS) as instrumental variables to test bidirectional causality between ADHD symptoms and school grades.
Limitations: Polygenic risk scores were trained only on European GWAS, limiting generalizability to other ancestries. · The DoC and MR-DoC models provided insufficient information to resolve directionality on their own. · Reliance on caregiver-reported data for both ADHD symptoms and school grades.

Summarized by Gemma 4 from the open-access full text · 9 Oct 2026. Read it