Up to 50% of children with ADHD experience motor impairment consistent with DCD. Debate continues as to whether this impairment is linked to inattention or is a genuine motor deficit. This study aimed to determine whether (1) inattention was greater in ADHD+DCD than in ADHD alone and (2) motor imagery deficits observed in DCD were present in ADHD+DCD. Four groups aged 7-12 years-ADHD, combined type, with motor impairment (ADHD+DCD; N=16) and alone (ADHD; N=14), DCD (N=10) and typically developing comparison children (N=18) participated. Levels of inattention did not differ between ADHD groups. On an imagined pointing task, children with DCD did not conform to speed accuracy trade-offs during imagined movements, but all other groups did. However, on a hand rotation task, both the ADHD+DCD and DCD groups were less accurate than the non-motor impaired groups, a finding not explained by differences in IQ, age, or working memory capacity. Overall, there was evidence that children with ADHD+DCD experience genuine motor control impairments indicating the impact of motor impairment in ADHD and its causal risk factors require more study. Motor impairment in ADHD should not be dismissed as a by-product of inattention.
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