Objective: Stimulant medications, such as methylphenidate (MPH), improve the academic performance of children with attention-deficit hyperactivity disorder (ADHD). However, the mechanism by which MPH exerts an effect on academic performance is unclear. We examined MPH effects on math performance and investigated possible mediation of MPH effects by changes in time on-task, inhibitory control, selective attention, and reaction time variability.
Methods: Children with ADHD aged 7 to 11 years (N = 93) completed a timed math worksheet (with problems tailored to each individual's level of proficiency) and 2 neuropsychological tasks (Go/No-Go and Child Attention Network Test) at baseline, then participated in a 4-week, randomized, controlled, titration trial of MPH. Children were then randomly assigned to their optimal MPH dose or placebo for 1 week (administered double-blind) and repeated the math and neuropsychological tasks (posttest). Baseline and posttest videorecordings of children performing the math task were coded to assess time on-task.
Results: Children taking MPH completed 23 more math problems at posttest compared to baseline, whereas the placebo group completed 24 fewer problems on posttest versus baseline, but the effects on math accuracy (percent correct) did not differ. Path analyses revealed that only change in time on-task was a significant mediator of MPH's improvements in math productivity.
Conclusions: MPH-derived math productivity improvements may be explained in part by increased time spent on-task, rather than improvements in neurocognitive parameters, such as inhibitory control, selective attention, or reaction time variability.
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*Department of Pediatrics, Cincinnati Children's Hospital Medical Center, Cincinnati, OH;
†Department of Psychology, University of Cincinnati, Cincinnati, OH;
‡Department of Psychology, Virginia Commonwealth University, Richmond, VA.
Address for reprints: Tanya E. Froehlich, MD, MS, Cincinnati Children's Hospital Medical Center, Mail Location 4002, 3333 Burnet Avenue, Cincinnati, OH 45229; e-mail: email@example.com.
Supported by the National Institute of Mental Health (R01MH074770 and K24 MH064478 [J.N.E.], K23 MH083881 [T.E.F.], and K23MH083027 [W.B.B.]).
The content is solely the responsibility of the authors and does not represent the official views of the National Institute of Mental Health or the National Institutes of Health.
Disclosure: The authors declare no conflict of interest.
Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions this article on the journal’s Web site (www.jdbp.org).
Received August , 2013
Accepted November , 2013