ADHD is a commonly diagnosed neuropsychological disorder among school-aged children with reported high rates of coexisting or comorbid disorders. As ADHD has been associated with academic underachievement, the current study examines this association in view of the presence of coexisting disorders. The purpose of the current study is to examine the relationship between the presence of coexisting disorders and academic achievement among children with ADHD using a large, nationally representative, and community-based sample. To achieve this purpose, the presence of coexisting disorders with ADHD and academic achievement are examined across time utilizing latent growth models. Our results indicate an inverse relationship between the presence of coexisting disorders and academic achievement across time among children diagnosed with ADHD. The authors conclude that practitioners must be concerned with the presence of coexisting disorders for children with ADHD with respect to academic achievement as well as other behavioral and psychological outcomes.