Fetal alcohol spectrum disorder (FASD), characterized by various levels of dysmorphia and behavioral and cognitive dysfunctions, is the result of prenatal alcohol exposure. FASD characteristics can be masked by many other conditions. As a result, early identification of FASD is often difficult, leading to a delay of children with FASD receiving necessary services. However, screening children with attention-deficit/hyperactivity disorder (ADHD), which is the major comorbid disorder of FASD, may enable the identification of children with FASD earlier than screening all children in schools. Therefore, the purpose of this study was to examine the differences between children with ADHD only and children with FASD and ADHD in terms of adaptive functioning, behavioral characteristics, and academic performance that impact school outcomes and can be recognized in classrooms. This study conducted a review of the medical records of 149 individuals with single ADHD diagnosis and 189 individuals with dual diagnosis of FASD and ADHD ( M [subscript age] = 11.25, SD = 2.12). Results of analysis of covariance analysis indicated: (1) no difference in adaptive functioning between the dual diagnosis group and the single diagnosis group, (2) the dual diagnosis group exhibited significantly more externalizing behaviors than the single diagnosis group, but the difference between the two groups regarding internalizing behaviors was not significant, (3) there was no significant differences between the two groups on reading and mathematics. Differences in characteristics between the two groups and implications for future research are also discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]