Anne Fleur Kortekaas-Rijlaarsdam

133 SUMMARY AND DISCUSSION 7 The results from our double-blind randomized placebo-controlled crossover study comparing the immediate (7-days treatment) effects of long-acting MPH and placebo are in line with the findings from the meta-analysis and were described in Chapter 3. Here, we investigated the impact of ADHD on academic performance and the effects of MPH on academic accuracy and productivity in math, reading and spelling. Children with ADHD (N=63, age 8-13, IQ>70) were impaired on math accuracy and productivity compared to TD children (N=67, age 8-13, IQ>70). The effects of MPH were small- to medium sized and limited to those academic subjects for which children with ADHD significantly underperformed in comparison to TD children (math). For mathematical productivity, MPH treatment resulted in a 2% increase, but performance did not normalize to the level of TD children. Further, MPH treatment increased accuracy for mathematical word problems by 9% and so doing normalized performance of children with ADHD to the level of TD children. Together, the results from the meta-analyses and our RCT reveal that academic improvements with MPH in children with ADHD are small compared to symptom improvements (which were medium- to large in this study) and qualitative improvements were limited to math. S E COND A I M The Mechanism behind MPH-effects on Academic Performance In the meta-analysis described in Chapter 2, we investigated the mediating and moderating effect of behavioral improvements (mediator) and demographic-, design-, and disorder-related variables (moderators). The number of studies reporting on these mediators and moderators was limited, therefore our meta-regression analyses were conducted for the effects of MPH on math accuracy only. Further, the number of studies reporting on on-task behavior and parent-rated improvements in ADHD symptoms was insufficient for meta-regression. Our results from the meta-regression of 29 studies on MPH effects on math accuracy reveal no mediating effect of teacher-rated ADHD symptom improvements. None of the included moderators (age, gender, ADHD- subtype, ODD/CD comorbidity, ADHD severity, release system, study duration, time of measurement, dose and titration method) affected the effect of MPH on academic performance. Thus, the meta-regression of existing studies reported provides no evidence for effects of the hypothesized behavioral mediators and demographic-, design-, and disorder related moderators. However, more research on this topic is necessary to investigate the effects of potential mediators and moderators on other academic outcomes (e.g. math productivity, reading accuracy and productivity).