Attention-deficitlhyperactivity disorder (ADHD) is one of the most common childhood disorders referred to mental health professionals. ADHD, a complex neurodevelopmental disorder, is seen in approximately 3-7% of school-aged children, with higher rates found among boys than girls (6: 1 in clinical settings, 3: 1 in community settings) in the United States (e.g., Barkley, 1998; Pastor & Reuben, 2002). In a review of estimates over a four-year period, Rowland, Leswesne, and Abramowitz (2002) found that prevalence rates varied substantially, based on presenting symptoms, assessment approaches used, and setting in which the child was evaluated. Furthermore, lack of consensus on what constitutes a core set of symptomology for ADHD children complicates the screening and assessment process (e.g., Brown et aI., 2001; Elia, Ambrosini, & Rapoport, 1999). Researchers contend that a coherent set of symptoms and causal factors does not exist, and this disorder represents a heterogeneous group of separate disorders (Neul, Applegate, & Drabman, 2003). For example, Goodman and Poillion (1992) identified 69 separate characteristics of ADHD, with 38 associated causes.