Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 7 134 In Chapters 3 and 4 we further investigated the mechanism behind MPH-related improvements in academic performance. Data was obtained from the abovementioned RCT investigating the short-term effects of MPH on academic performance in a group of children with ADHD. Specifically, the mediator and moderator analyses in these chapters focused on math productivity and math accuracy as these measures showed significant (albeit small) improvement with MPH treatment. In Chapter 3, we investigated the mediating effect of ADHD symptom improvements on the relation between MPH treatment and math performance. In addition, this chapter describes the moderating effects of learning ability and ADHD symptom severity on MPH- related math improvements. In line with our hypothesis, parent-rated symptom improvements partially mediated the effects of MPH on math productivity. Parent- rated symptom improvements did not affect MPH-improvements in math accuracy. Also, teacher-rated improvements in ADHD symptoms did not influence MPH-effects on math accuracy or math productivity. The former is in line with the results from the meta-analysis. Moreover, MPH efficacy in improving math accuracy in this study was limited to children with lower-than-average mathematical abilities. Our results implicate that ADHD symptom severity (attentional and hyperactive/impulsive symptoms) did not moderate the effects of MPH on math performance. Thus, the results from Chapter 3 suggest that the small effects of MPH on math performance are, at least in part, due to improvements in ADHD symptoms. In Chapter 4, we expanded the findings of Chapter 3 by exploring the mediating effects of MPH-related improvements in cognition, motivation and perceived competence on MPH effects on math performance. The results from this study indicate that children with ADHD perform worse than TD children on cognitive measures thought to be important in determining academic performance, including visuospatial working memory and lapses of attention. Moreover, children with ADHD showed lower intrinsic motivation for schoolwork, specifically for math. In addition, children with ADHD showed altered parent-rated reward responsivity and lower self-, parent- and teacher rated self-perceived competence. In contrast to our hypotheses, MPH improved neither cognition nor motivation for schoolwork. Thus, this study did not provide evidence for a mediating role for cognitive or motivational improvements on MPH-related effects on math. Our results did show that MPH increased parent-ratings of their child’s self- perceived competence and these improvements mediated MPH efficacy on math productivity. Together, the results from our RCT demonstrate that the limited effects of MPH on math productivity are at least partly due to behavioral improvements, whereas such behavioral improvements (teacher- and parent-rated) do not affect MPH effects on math accuracy. Further, the results from Chapter 4 raise questions about