Adapted methods of behavioral assessment to assess home and school functioning in a way that maps directly to the Diagnostic and Statistical Manual of Mental Disorders (4th ed., [DSM-IV]; American Psychiatric Association, 1994). The study was conducted in a school-based sample with 5- to 12-year-old children referred to a school intervention team. A multigate set of procedures was used to assign children to one of 3 groups: attention deficit hyperactivity disorder (ADHD), inattentive group; ADHD, combined group; and a non-ADHD control group. The ADHD Rating Scale-IV was used to assess parent and teacher ratings of ADHD symptoms as delineated in DSM-IV. The findings suggest that the use of a fixed cutoff point (i.e., 6 or more symptoms), which is employed in the DSM-IV, is often not the best strategy for making diagnostic decisions. The optimal approach depends on whether diagnostic information is being provided by the parent or teacher and whether the purpose of assessment is to conduct a screening or a diagnostic evaluation. Also, the results indicate that a strategy that aggregates symptoms in the order in which they are accurate in predicting a diagnosis of ADHD is a more effective strategy than the approach used in DSM-IV, which aggregates any combination of a specific number of items. Implications for using methods of behavioral assessment to make diagnostic decisions using DSM-IV criteria are discussed.