Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 4 90 D I SCUSS I ON In the current study, we investigated the effects of methylphenidate on cognitive functions important for learning, academic motivation and perceived academic competence. To better understand the limited and selective academic medication- related improvements in children with ADHD (Langberg & Becker, 2012; Prasad et al., 2013) we aimed to identify possible mediators of methylphenidate-related improvements in math performance. Our results corroborate with earlier studies in showing that children with ADHD not only underperform in comparison to their TD peers on school subjects (DuPaul, 2007; Kortekaas-Rijlaarsdam et al., 2017b), but also perform worse on cognitive measures important for academic performance. More specifically, we found children with ADHD to be impaired in terms of visuospatial working memory and lapses of attention (Mullane et al., 2009b; Willcutt et al., 2005). Furthermore, children with ADHD were found less motivated for schoolwork, specifically for math, in line with previous reports (Carlson et al., 2002). In addition, our results confirm that children with ADHD may be somewhat more sensitive to punishment and reward than TD children (Luman et al., 2005). Moreover, self- perceived competence (according to children, their parents and their teachers), was lower for the ADHD group than for the TD group, which corroborates the previous finding of a negative relationship between ADHD symptoms and self-perceived competence (Scholtens et al., 2013). Although group differences in cognitive performance and academic motivation between our ADHD group and the TD group were large and previous literature reports positive effects of MPH on cognition and motivation for learning, our results tone down the importance of these variables in the explanation of MPH-related academic improvements. In spite of testing an elaborate set of relevant cognitive and motivational variables overall we found no improvements in cognition and motivation with MPH compared to placebo. As our ADHD group clearly underperformed on the selected variables in comparison to TD peers, it is unlikely that these results are due to lack of room for improvement in our ADHD group. We also trust that the absence of effects is not due to lack of power, as we had sufficient power to detect medium sized effects which seems suitable for the selected cognitive variables based on a recent meta-analysis (Coghill, Seth, et al., 2014). In addition, standardized mean differences of the effects of MPH on cognition and motivation are small (mostly <.05), supporting the idea that our results are not due to a lack of power. Further, we investigated a specific set of cognitive measures (working memory, reaction time, lapses of attention and interference control), which are often affected in children with ADHD and related to academic