Research Project III Summary Building on extensive past research by Project III on the comorbidity of reading disability (RD) and ADHD, the proposed research will extend those methods and concepts to understanding the comorbidities among less-studied complex LDs, and their comorbidifies with ADHD and with RD. Project III will use multiple methods of analysis to examine how component cognitive skills, including executive funcfions (EFs), contribute to these comorbidities. Previous research has demonstrated that ADHD is comorbid with each of these less-studied LDs, including poor reading comprehension, poor written language, and poor math problem solving ability, and considerable prior research indicates a role for EFs in these disorders. Proficiency in these academic skills requires not only mastery of prerequisite basic skills, but also higher level-thinking skills, such as oral language comprehension and EFs. Project III will explicitly test versions of this interactive model of these three complex LDs in collaboration with Projects II and V. So the goal of Project III is to gain a comprehensive understanding ofthe comorbidifies among these three complex LDs and their comorbidifies with both ADHD and RD. In collaboration with Project I, Project III will also confinue ongoing wori< on the comorbidity between dyslexia (RD) and ADHD. Project III will test these comortDidities at both the cognifive and efiological levels of analysis. It will also test whether GxE interactions are part ofthe etiology of these disorders and their comorbidifies. Even though there is considerable evidence for shared cognitive and genefic risk factors across these disorders, their relations have not been previously examined in the same sample. RELEVANCE (See instructions): Project III will examine the comorbidity among complex LDs and their comorbidifies with RD and ADHD in the same sample. The resulting increased understanding of complex LDs will sharpen the focus of eariy idenfificafion and prevenfive intervention. Efiological or cognitive risk factors that are shared by multiple LDs and ADHD should provide a particularly important target for early intervention.