The effect of processing speed on academic fluency in children with neurodevelopmental disorders

Poor processing speed (PS) is frequently observed in individuals with neurodevelopmental disorders. However, mixed findings exist on the predictive validity of such processing speed impairment and the role of working memory (WM). We conducted a retrospective chart review of patients evaluated at a developmental assessment clinic between March 2018 and December 2022. Patients with available data on the Wechsler Intelligence Scale for Children, Fifth Edition (WISC-V) and the Woodcock-Johnson, Fourth Edition, Tests of Achievement (WJ IV ACH) were included (n = 77, 69 % male; M_age = 10.6, SD_age = 2.5; FSIQ range = 47–129). We performed a mediation analysis with academic fluency (AF) as the dependent variable, PS as the predictor, WM as the mediator, and academic skills and general intelligence as covariates. Both the direct and indirect effects of PS were significant prior to adding covariates. However, only the direct effect of PS was robust, independent of the effects of academic skills and general intelligence. The indirect effect of PS through WM was insignificant after accounting for the general academic skills and intelligence. Therefore, PS explains a unique variance in AF. This finding suggests that PS may be an exception to the criticism of cognitive profile analysis. Interpreting the PS score as a relative strength or weakness within a cognitive profile may uniquely predict their timed academic performance in youth with neurodevelopmental disorders.