Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 7 146 (including medication dose, duration of treatment, type of medication) and mediators (such as improvements in cognition or motivation) of MPH is necessary as data is currently too limited for meta-regression. When possible, these future studies should include a baseline measurement without medication to further clarify the interpretation of MPH-effects on academic performance because placebo effects are generally large, with effect sizes >.40 (Krogsbøll et al., 2009). In addition, the results from our meta-analysis reveal that MPH-effects on math performance are not affected by release system (i.e. immediate versus extended release or transdermal patches). This is in line with individual studies comparing the effects of immediate- and extended release MPH on academic performance (Döpfner et al., 2004; Pelham Jr. et al., 1990; Swanson et al., 2004), and this is promising given the increasing popularity of extended release formulations. There are however, also differences between extended release stimulants. For example, extended release formulations of MPH often have a component that is released immediately after it is taken. The relative size of this component differs between formulations (Banaschewski et al., 2006). It is therefore important that treating physicians are aware of these differences so they can optimally adjust medication type to individual needs of the child. For example, when a child experiences difficulties during the start of the school day a larger immediate component may be considered whereas for another child a more equally distributed release over the day may be preferred. Moreover, our results suggest that MPH-related improvements in parent-rated self- perceived academic competence mediate MPH effects on math productivity. These results need to be replicated and expanded if we are to further understand the role of parent-rated self-perceived competence in relation to motivation and performance. In addition, future research should look into the differences between self-, parent- and teacher-ratings of MPH-improvement so we can further understand the surprising finding that only parent-rated measures mediate MPH-effects on academic performance. Concerning instrumental learning and learning under different motivational conditions, the results from this thesis suggest that correct acquisition of novel knowledge does not guarantee that a child with ADHD can apply such knowledge elsewhere. As this application of knowledge in different and novel situations is daily practice in the life of a child with ADHD, future research should further investigate the potential of MPH to improve this. In addition, our results emphasize the relevance of task motivation for performance. Teachers and parents should realize that, for