Reading abilities and cognitive processing in grade 3 children with ADHD comorbid with developmental dyslexia.

Attention Deficit/Hyperactivity Disorder (ADHD) frequently co-occurs with developmental dyslexia (DD) (ADHD + DD). Children with ADHD + DD manifest low achievement in reading performance and cognitive abilities. There is, however, a lack of research exploring the association between reading abilities and cognitive processing based on the Planning-Attention-Simultaneous-Successive (PASS) theory, particularly in those with ADHD + DD and ADHD subtypes (e.g., the predominantly inattentive subtype (ADHD-I), predominantly hyperactive/impulsive subtype (ADHD-H), and combined subtype (ADHD-C)). In this study, we enrolled a total of 318 grade 3 children (including 99 ADHD + DD, 103 ADHD-I, 7 ADHD-H, 22 ADHD-C and 87 typically developing (TD) children), all of whom were assessed on measures of reading ability and Das-Naglieri Cognitive Assessment System (DN: CAS). Our key findings reveal that ADHD + DD have an imbalance in their intelligence structure, showing a certain advantage in Performance IQ, while their Verbal IQ tends to be relatively weaker. In terms of DN: CAS cognitive processing, children with ADHD-H exhibit impairments exclusively in Planning, while other cognitive domains remain intact. ADHD + DD children not only exhibit the typical characteristics of ADHD, but also show these traits in a more severe, including deficits in Successive processing. Regression analysis revealed that Successive processing might negatively affect character recognition in children with ADHD + DD. The study highlights that in the context of severely low Attention and Planning processing, Successive processing plays a very different and even negative role in reading ability. This needs to be taken into account when designing remedial interventions for children with ADHD + DD.