Objectives: (1) To determine the processing speed (PS) deficit in children with ADHD; and (2) To investigate if PS deficit was the primary cause of daily dysfunction in ADHD by testing the direct and indirect effects via working memory (WM) of PS on math fluency (MF).
Method: Seventy-eight children (52 children with ADHD and 26 controls) were tested on their motor, perceptual, cognitive, and verbal PS, WM, and MF.
Results: Children with ADHD performed worse than controls on all PS, suggesting a general PS deficit. Moreover, cognitive PS was a significant predictor for MF. Mediation analysis showed that cognitive PS had direct and indirect effects via WM on MF, suggesting PS deficit might be the primary cause of MF difficulties in ADHD.
Conclusion: Findings of this study suggested a general PS deficit in ADHD. Due to the importance of PS in MF, interventions for MF underachievers should include assessment and training of PS.
Keywords: ADHD; math fluency; processing speed; working memory.