In our clinical experience, behavioral scales tend to be overrated in Attention-Deficit Hyperactivity Disorder (ADHD) diagnostic procedures. Our main goal is to demonstrate, through two schoolchildren's clinical cases, the contributions of neuropsychological evaluations towards the diagnosis of ADHD. We consider that the diagnosis must be essentially clinical, which means that it can not be done solely based on any scale or test. The attention process consists of several interactive functions while the deficit itself indicates a syndromic scenario, not a specific disease. As so, attention deficit may manifest itself as a primary clinical picture or as a secondary symptom to several disorders and circumstances. Several contradictions were found between the evaluations of behavioral scales, such as the Benczik and DSM IV scales, and other ones based on neuropsychological criteria, such as WISC-III.