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

Abstract Attention-deficit/hyperactivity disorder (ADHD) symptoms are strongly associated with lower academic performance, yet the nature of this association remains uncertain. We analyzed data from twins and siblings in the Adolescent Brain Cognitive Development (ABCD) Study ® to examine the relationship between ADHD symptoms and school grades using genetically informed models. ADHD symptoms were assessed via the Child Behavior Checklist, and grades were caregiver-reported for the previous school year. Both phenotypes were modeled as ordinal variables. We applied Direction of Causation (DoC) and Mendelian randomization extensions (MR-DoC and MR-DoC2) incorporating polygenic risk scores for ADHD and educational attainment. DoC and MR-DoC comparisons did not distinguish directionality (e.g., DoC forward path estimate = − 0.16, 95% CI [− 0.26, − 0.07]; reverse path = − 0.30, 95% CI [− 0.63, − 0.17]). In MR-DoC2, estimates differed in precision: ADHD-to-grades path = − 0.31, 95% CI [− 0.62, − 0.11]; grades-to-ADHD path = − 0.60, 95% CI [− 1.20, 0.03]. Sex-limitation tests indicated no moderation by sex.