Anne Fleur Kortekaas-Rijlaarsdam

11 INTRODUCTION 1 years of education ( d =.56) and higher drop-out and grade repetition ( d =.49). Higher effect sizes for standardized achievement tests can be explained by the negative effects of ADHD on test-taking behaviors (Reaser & Reaser, 2007; Zwart & Kallemeyn, 2001). However, the impact of ADHD diagnosis on longer-term outcomes imply that the negative effects of ADHD go beyond negative tests-taking behaviors to actual academic impairments. More recently, Arnold et al. (2015) synthesized 176 studies reporting on standardized achievement tests and long-term academic outcomes of individuals with ADHD. Their results are in line with Frazier et al. (2007), indicating negative effects of ADHD diagnosis on standardized achievement test (especially math and reading) and negative effects of ADHD on length of schooling. In addition, results from Arnold et al. (2015) indicate that ADHD also negatively affects type of schooling (level of education; the need for remedial teaching or special education). The consequences of the academic impairments of children with ADHD are severe: Failing to complete high school, lower job performance and attainment. In addition, and possibly as a result of these, individuals with ADHD report more social problems and lower quality of life (Barkley et al., 2006; Coghill et al., 2008; Frazier et al., 2007; Loe & Feldman, 2007). Factors Contributing to Academic Impairments in ADHD Children with ADHD experience a wide range of problems within the classroom. For example, children with ADHD show more task-irrelevant behaviors (e.g. fidgeting, wiggling, daydreaming or oppositional behaviors) related to their inattention and hyperactivity-impulsivity (DuPaul et al., 2004). Evidence for the negative impact of ADHD (behavioral) symptoms is especially strong for symptoms of inattention but also apparent for hyperactivity-impulsivity symptoms (Polderman, Boomsma, Bartels, Verhulst, & Huizink, 2010). Specifically, inattention symptoms were predictive for impaired performance on academic achievement tests (math, reading, spelling), were less likely to graduate from high school and more often failed to continue to college. Hyperactivity-impulsivity symptoms were also associated with impaired performance on achievement tests, but also with failure to graduate from high school, less years of education, lower grades and higher need for special education. Negative effects of ADHD symptoms were apparent in children as well as adolescents and young adults, in line with findings from other aggregations of literature (Frazier et al., 2007). Theoretically, ADHD symptoms and impairments are hypothesized to arise from both cognitive and motivational deficits. An important causal model of ADHD, the dual- pathway model, argues that cognitive and motivational problems of children with ADHD independently (though separate pathways) impact behavior of these children (Sonuga-Barke, 2003, 2005). Therefore, in addition to impaired school performance