Written expression in boys with ADHD: The mediating roles of working memory and oral expression

ABSTRACT

The written expression difficulties experienced by children with ADHD are widely recognized; however, scant empirical evidence exists concerning the cognitive mechanisms and processes underlying these deficiencies. The current study investigated the independent and potentially interactive contributions of two developmentally antecedent cognitive processes – viz., working memory (WM) and oral expression – hypothesized to influence written expression ability in boys. Thirty-three boys with ADHD-Combined Presentation and 27 neurotypical (NT) boys 8–12 years of age were administered standardized measures of oral and written expression, and multiple counterbalanced tasks to assess WM central executive (CE) processes, WM phonological short-term memory (PH STM), and WM visuospatial short-term memory (VS STM). Bias-corrected bootstrapped mediation analyses revealed a significant mediation effect, wherein the independent and interactive effects of PH STM and oral expression collectively explained 76% of the diagnostic status to written expression relation. The implications of the obtained results for clinical practice suggest that children with ADHD may benefit by incorporating a blended approach that simultaneously strengthens PH STM capacity and oral expression abilities as antecedents to engaging in writing-related activities.

KEYWORDS:

• Attention-deficit/hyperactivity disorder (ADHD)
• working memory
• written expression
• oral expression
• executive functions

Disclosure statement

The authors declare that they have no conflicts of interest.

Notes

¹ PH WM and VS WM performance data for a small subset of the current sample were used in previous studies (references masked for review) to examine conceptually unrelated hypotheses. The associations among the Written Expression, Oral Expression, and WM tasks used in the current study have not been examined previously.

² Criteria for a learning disorder (LD) in written expression was defined by a Standard Score (SS) of more than 1 SD (15) below the normative mean (i.e., SS < 85) on the KTEA-II Written Expression subtest. The association between diagnostic status and written expression was not moderated by the presence of a LD in written expression (p = .92). Further, although 15 ADHD children received educational accommodations, the presence of such interventions did not moderate (p = .62) the diagnostic status/written expression relation.

³ Alternative approaches were considered but not adopted because they also share substantial variance with WM (e.g., the WISC-IV and -V General Ability Index [GAI] is comprised of the Verbal Comprehension and Perceptual Reasoning Indices, and shares 25% to 40% of variance with WM, respectively).

⁴ A defining feature of the parallel multiple mediation model is the constraint that each potential mediator is modeled controlling for (holding constant) all other mediators in the model to allow competing hypotheses of mechanisms or processes to be examined independently of one another (Hayes, 2018).

Additional information

Funding

This study was conducted without external funding.