Anne Fleur Kortekaas-Rijlaarsdam

127 EFFECTS OF MPH AND REWARD ON MATH PERFORMANCE 6 competence and reduce feelings of (math related) anxiety (Hattie & Timperley, 2007), possibly resulting in better academic outcomes (Linnenbrink & Pintrich, 2002; Spinath et al., 2006). Interestingly, these findings oppose recent findings indicating that learning without feedback may be advantageous in the longer term, as it may result in better retaining of the learned information (Fyfe & Rittle-Johnson, 2017). Thus, more research on the longer term effects of reward and feedback on academic performance is needed to extend our findings. In line with our expectations, the combined effects of rewarded feedback and MPH on math performance were larger than either treatment alone. Effect sizes of independent effects were small- to medium sized for rewarded feedback and MPH treatment, respectively. In contrast, the effect size of the combination of rewarded feedback and MPH was large. These findings corroborate findings from previous studies on this topic (Pelham et al., 1986; Rosch et al., 2016; Strand et al., 2012). Both increased motivation (by rewarded feedback) and MPH treatment improved math performance in children with ADHD, which is in line with literature on the effects of reward on math-related cognitive functions (Dovis et al., 2012), as well as with previous studies on the effects of MPH on math performance (Kortekaas-Rijlaarsdam et al., 2018). It is promising that the effects of rewarded feedback and MPH on math performance are additive, given the need for improvement in this area, especially for children with ADHD (Frazier et al., 2007). The effects of rewarded feedback and MPH on math performance did not interact, which implies that MPH treatment does not affect the ability to profit from rewarded feedback on a math task. Thus, the effects of rewarded feedback and MPH on math performance are independent. This finding contrast the view that MPH treatment normalizes the altered reinforcement threshold of children with ADHD, but is in line with findings from Rosch et al. (2016) who also showed additive effects of rewarded feedback instead of an interaction between these effects. Importantly, both rewarded feedback and MPH treatment resulted in normalization of math performance of children with ADHD compared to TD children. Thus, our result imply that the use of rewarded feedback is equally effective as MPH in improving math performance in children with ADHD. The finding that reward and MPH can independently normalize academic performance of children with ADHD to the level of their TD peers is in line with comparable studies using cognitive outcome measures (Rosch et al., 2016). This finding emphasizes the efficacy of motivational strategies such as rewarded feedback to improve academic performance, thereby reducing the