ADHD symptoms and learning difficulties: co-occurrence and directionality from Grades 1 to 9

Children with attention-deficit/hyperactivity disorder (ADHD) are at increased risk of learning difficulties. This association may reflect shared risk factors, ADHD symptoms hindering learning, or learning difficulties increasing ADHD symptoms. We aimed to map rates of co-occurrence among ADHD, dyslexia, dyscalculia, and reading comprehension difficulties and to investigate directional influences between ADHD symptoms and reading fluency, arithmetic, and reading comprehension.

Reading fluency, arithmetic, and reading comprehension were assessed longitudinally in approximately 2,000 Finnish children across Grades 1-9 (ages 7-16). Attention/hyperactivity symptoms were measured with teacher ratings (Grades 1-4) and self-reports (Grades 6-9). ADHD, dyslexia, dyscalculia, and reading comprehension difficulties were based on a 10th percentile cut-off. Directionality between ADHD symptoms and academic skills was examined using random intercept cross-lagged panel models (RI-CLPMs) to separate stable traits from time-specific states.

Children with a learning difficulty were 1.14-1.76 times more likely to have ADHD, whereas children with one learning difficulty were 4.32-4.62 times more likely to have another. The RI-CLPMs showed consistent autoregressive effects across all domains, indicating stable within-person variation over time. At the between-person level (i.e. trait), academic skills were negatively related to ADHD symptoms, especially those reported by teachers. At the within-person level (i.e. state), ADHD symptoms were unrelated to reading fluency and arithmetic. However, at multiple time points, cross-lagged effects emerged from ADHD symptoms to subsequent reading comprehension, indicating that elevated ADHD symptoms predicted subsequent declines in reading comprehension.

Learning difficulties co-occurred more frequently with each other (homotypic) than with ADHD (heterotypic co-occurrence). Both ADHD symptoms and learning difficulties showed trait-like stability. After accounting for these, ADHD symptoms were no longer linked to reading fluency or arithmetic. However, more ADHD symptoms predicted later declines in reading comprehension, likely because comprehension requires sustained attention - often impaired in children with hyperactivity and inattention.