Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 3 70 ( N = 24) ( t (51) = 4.32, p = <.001), with a small effect size ( d = .24) , while the effect was not significant for children with above average mathematical abilities ( N = 39) (t(10) = .21, p = .841, d = .03). For mathematical word problem accuracy, mathematical ability (as measured by performance on mathematical word problems during the placebo condition) moderated the effect of medication ( χ 2 (1) = 10.75, p = .001). Post-hoc analysis with groups split on the mean z-score on mathematical word problem performance, showed that only children with below average mathematical abilities ( N =17) demonstrated significant improvement in accuracy with a large effect size ( t (16) = 3.95, p = .001, d = 1.16), whereas this effect was not significant for children with above average mathematical abilities ( N =44) ( t (41.4) = 1.41, p = .166, d = .13). The possible moderator ADHD symptom severity (attentional- and hyperactive/ impulsive symptoms on DISC-P) did not interact significantly with either mathematical productivity or mathematical word problem accuracy (all p -values between .253 and .936). This indicates that ADHD symptom severity did not influence the effects of methylphenidate on mathematical accuracy and productivity. To ensure that age did Figure 3.2 Moderating effects of mathematical ability on SAT productivity and mathematical accuracy on WP. Panel A shows the moderating effect of mathematical ability (as measured by SAT performance with placebo: above average (N=39) versus below average (N=24)) on the beneficial impact of methylphenidate on SAT productivity. Panel B shows the moderating effect of mathematical ability (as measured by WP performance with placebo: above average (N=44) versus below average (N=17)) on the beneficial impact of methylphenidate on mathematical accuracy on WP. SAT Speeded arithmetic test; TD Typically developing children; PLA Placebo; MPH Methylphenidate.