Words Don’t Come Easy : Decoding and Reading Comprehension Difficulties in Adolescents with Intellectual Disability

Sammanfattning: Individuals with intellectual disability (ID) have difficulties with decoding and reading comprehension. However, studies focussing on why these difficulties occur are very sparse, and the existing literature has found conflicting results. This thesis investigated the development of reading abilities and the concurrent cognitive, linguistic, and environmental predictors of decoding and reading comprehension in Swedish adolescents with ID of unknown aetiology. In addition, this thesis evaluated the applicability of one of the most commonly used theoretical frameworks of reading comprehension: the Simple View of Reading (SVR). The results showed that the development of reading abilities in adolescents with ID is in line with the model of developmental delay. This means that the development of reading abilities is not qualitatively different from typical reading development, but the rate is slower. Further, it means that the pattern of concurrent predictors is similar to the pattern found in a younger typically developing population. In Swedish adolescents with ID decoding is predicted by phonological awareness and rapid automatized naming (RAN), and reading comprehension is predicted by decoding, vocabulary, and phonological executive-loaded working memory (ELWM). This thesis also found that the developmental trajectory of decoding plateaus at a mental age of 8:9 years, while it is expected in typically developing children that decoding ability continues to increase until early adolescence. The explanation for this early plateau could be either cognitive or educational, but most likely a combination of both. Lastly, the results from this thesis also suggest that the SVR is not sufficient for explaining reading comprehension in adolescents with ID. Instead, a combination of the SVR and the Lexical Quality Hypothesis (LQH) is suggested as a successful way of explaining the variance in reading comprehension. Taken together, the results from this thesis implies that reading instruction and interventions originally developed for typically developing children is likely to be effective for individuals with ID.