Anne Fleur Kortekaas-Rijlaarsdam

139 SUMMARY AND DISCUSSION 7 educational outcomes of children with ADHD. The explanation for the discrepancy between effects of MPH on behavior (ADHD symptoms) and academic performance may lie in clinical titration practices. Medication is titrated on behavioral outcomes (parent- and teacher-ratings of ADHD symptoms), not on cognitive or academic outcomes. However, previous research suggests that medication dose optimal for ADHD symptom improvements is higher than optimal dose for cognitive improvements (Hale et al., 2011). These findings are in line with the smaller effects sizes (often medium sized) for cognitive improvements than for behavioral improvements (Coghill, Seth, et al., 2014; Pietrzak et al., 2006; Van der Oord et al., 2008). In our meta-analysis, we included studies using clinical titration methods as well as studies comparing fixed doses (high versus low). Because we aimed to investigate the maximum possible effects of MPH we selected the doses optimal for academic performance from the latter group. However, this was only possible for 9 out of 34 studies. It is therefore likely that medication doses in the other studies as well as in our RCT were suboptimal for cognitive and academic improvements. Evaluation of the Proposed Mediation Model The second aim of this thesis was to unravel the mechanism behind MPH-related improvements in academic performance. The results from our meta-analysis (Chapter 2) and RCT (Chapters 3 and 4) imply that our proposed model was largely incorrect. Although we found evidence for a mediating role for parent-ratings of ADHD symptoms and parent-ratings of their child’s perceived competence, our other mediators and moderators were not significant, see Figure 7.1. This is surprising given the impact of these variables on academic performance and that children with ADHD are impaired on these variables. It is important to note here that the actual effects of MPH on academic performance were minimal. Consequently, this reduces the importance of the mechanism behind such improvements and limits the potential influence of these potential mediators and moderators. Together, these results suggest that improvements in academic productivity at least partly depend on reductions in ADHD symptoms, whereas behavioral improvements do not result in qualitative improvements in academic performance per se.