Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 4 92 a better predictor of academic performance than self-reported intrinsic values. However, previous research focused on child-ratings (self-ratings) of self-perceived competence, whereas we find MPH-related improvements in parent-rated self- perceived competence. We focused on parent-ratings because such ratings may be more reliable than ratings done by the young children included in the study. More research on this topic is necessary. In addition, it is important to consider whether the way a cognitive process was assessed influenced our findings. – i.e., laboratory task measures versus parent-/teacher- or self-report questionnaires. Perhaps questionnaires are more sensitive in general compared to tasks. Future studies should include questionnaire-based measures tapping the same processes as the tasks. Furthermore, for ethical reasons our trial had a limited duration of two weeks and therefore results do not necessarily generalize to long-term academic outcomes. However, within this short period, significant improvements in parent-rated self-perceived competence were apparent and MPH resulted in improvements on most cognitive, motivation and competence measures. It might be speculated that a longer-term trial may result in additional improvements in cognition and motivation, for example resulting from improved competence (Wigfield & Eccles, 2000). To maximize ecological validity, we included children after titration by their treating physician following current standard clinical guidance. This may, however, have resulted in lower methylphenidate efficacy compared to double-blind titration procedures (MTA-group, 1999b). Furthermore, all participants were already treated with MPH, therefore it is hard to distinguish between acute and chronic effects of MPH. Baseline measures (without MPH or placebo) were not part of the current design. As placebo-effects of MPH are usually strong in studies with comparable duration (Krogsbøll, Hróbjartsson, & Gøtzsche, 2009), this could explain the absence and magnitude (small) of effects in our study. Adding a baseline measure in future studies may help clarify the interpretation of MPH effects on cognitive performance further. In addition, although our questionnaires on motivation and perceived competence have good psychometric qualities, this is the first study that investigates the impact of stimulants on these questionnaire scores. Therefore, their sensitivity to detect stimulant effects is still unknown. In conclusion, our results confirm that ADHD is associated with deficits in working memory, increases in lapses of attention, lower academic motivation and lower perceived competence, variables that have proven important for school performance. Our results tone down the importance of cognition and motivation in the explanation of MPH-related improvements in academic functioning. Short-term MPH-related