Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 3 72 Tirosh, 2008; Douglas et al., 1986). The absence of effects of methylphenidate on reading and spelling may be due to the fact that our participants with ADHD did not underperform in reading and spelling compared to TD children when receiving placebo, which is in contrast with previous findings indicating underperformance in reading comprehension for children with ADHD (Loe & Feldman, 2007). In the current study we investigated technical reading, not reading comprehension. Although both are essential skills learned in primary school, reading comprehension may be more sensitive to methylphenidate-related improvements as reading comprehension is more dependent on vocabulary and spatial intelligence than technical reading (Aarnoutse & van Leeuwe, 1988). Indeed, earlier studies show effects of methylphenidate on spatial intelligence (e.g., spatial working memory tasks (Coghill et al., 2014). This may explain the absence of methylphenidate-effects on reading. Our hypothesis about a partially mediating role for symptom improvement on methylphenidate effects for academic performance was confirmed: Methylphenidate-related improvements in math productivity were related to reductions in parent-rated ADHD symptoms. To our knowledge, no previous studies have investigated the explanatory value of behavioral improvements on medication-effects on school performance. Related to our findings are the results of Froehlich et al. (2014), showing a mediating role for a proxy of classroom behavior (on-task) on the effects of methylphenidate on math productivity on a task comparable to the SAT. Their results already suggested a partially mediating role for improvements in classroom behavior, but our study confirmed that this effect is also observed when looking at ADHD symptom improvement. Parent-rated symptom improvements only mediated the effects of methylphenidate on math productivity not on accuracy. This may be because mathematical word problems are more challenging than speeded arithmetic (Froehlich et al., 2014) and therefore improvements in behavior may not be sufficient to also improve accuracy on such a task. In contrast to our expectations, only parent-rated symptom improvement, but not teacher-rated symptom improvement, mediated medication effectivity. Possibly parents are better able to detect more subtle changes in their child’s behavior than teachers are, as parents generally spend more time with their child, which probably makes parents a more valid source of information for behavioral improvements in different settings (Shemmassian & Lee, 2012). The beneficial effects of methylphenidate on mathematical productivity and accuracy were found to be moderated by mathematical ability, as only children with below average mathematical abilities showed a significant improvement with methylphenidate, whereas children performing above average did not improve on either productivity or accuracy. Our findings suggest that lower mathematical abilities may predict better treatment