Anne Fleur Kortekaas-Rijlaarsdam

CHAPTER 3 58 (Baweja et al., 2015). Moreover, the long term effects of stimulant medication for ADHD remain to confirmed (Arnold et al., 2015; Langberg & Becker, 2012): Such improvements are mostly found for standardized achievement tests rather than school grades and/or rates of school drop-out or retention. Medication-related improvements in test-taking behavior in standardized settings may have a greater impact on standardized achievement tests than on school grades. However, effect sizes for standardized achievement tests are small and medication did not result in normalization of academic performance (Langberg & Becker, 2012). Also, improvements in academic performance are larger with multimodal interventions than with medication treatment alone (Arnold et al., 2015). Although numerous placebo-controlled controlled trials have investigated the impact of methylphenidate on school performance, studies vary greatly in methodology. For example, dosages prescribed are often fixed and not clinically titrated, which reduces ecological validity (Prasad et al., 2013). Also, the academic tasks used are often not validated (Douglas et al., 1986; Froehlich et al., 2014; James et al., 2001; Pelham et al., 1985; Tannock, Schachar, Carr, & Logan, 1989). In addition, laboratory schools are often used as research settings which may reduce the ecological validity of the study. Furthermore, studies of the efficacy of long-acting methylphenidate on academic performance are scarce (Prasad et al., 2013) even though there is an increase in the prescription of long-acting methylphenidate. Long-acting methylphenidate results in more constant blood plasma levels during the day, and thus fewer rebound effects, which may result in better academic performance compared to immediate release methylphenidate (Banaschewski et al., 2006). Moreover, more knowledge about variables mediating and moderating the effects of methylphenidate on academic performance is needed. Such knowledge is essential to explain the mechanism behind medication efficacy and to identify clinical subgroups for which higher or lower efficacy may be expected. ADHD is a heterogeneous disorder with large differences in symptom severity and high comorbidity with 30% of children with ADHD suffering from learning disorders (Williamson et al., 2014). Additional comorbid learning disorders often result in worse educational outcomes than ADHD alone (Faraone et al., 2001). Differences in symptom severity and learning problems may influence treatment effectivity, and individual differences in treatment response within the ADHD population may explain the absence of robust effects of stimulant medication on academic performance at the group level (Langberg & Becker, 2012; Prasad et al., 2013). So far, only a few studies focussed on potential mediators and moderators when studying methylphenidate