This collection of papers focuses on definitions, assessment, assessment instruments, and distinctions between attention deficit disorder (ADD) and general learning disabilities or conduct disorders. Part I covers issues of definition and assessment in the following papers: "Methodological Issues in the Classification of ADD" (Jack Fletcher, et al.); "The Yale Children's Inventory: Normative Data and Their Implications for the Diagnosis of ADD in Children" (Sally Shaywitz, et al.); and "School-Based Assessment of Attention Deficit-Hyperactivity Disorder" (Marc Atkins and William Pelham). Part II examines distinctions within and across disorders in the following: "Validity of the Diagnostic Category of ADD Without Hyperactivity: A Review of the Literature" (Benjamin Lahey and Caryn Carlson); "Association Between Attention Deficit-Hyperactivity Disorder and Learning Disorders" (Dennis Cantwell and Lorian Baker); "ADD and Specific Reading Disability: Separate but Often Overlapping Disorders" (Roscoe Dykman and Peggy Ackerman); "The Effect of Extra Time on Reading Comprehension Scores for University Students With and Without Learning Disabilities" (M. Kay Runyan); and "The Boundaries of ADD" (Mark Epstein, et al.). Part III addresses the neurobiology of ADD in "Cognitive Event-Related Potentials in ADD" (Rafael Klorman) and "Corpus Callosum Morphology in Attention Deficit-Hyperactivity Disorder" (George Hynd, et al.). The final section focuses on treatment in the following: "Cognitive Training in ADHD Children: Less to It Than Meets the Eye" (Howard Abikoff);"Stimulant Medication and Parent Training Therapies for Attention Deficit-Hyperactivity Disorder" (Arthur Anastopoulos et al.); "Effects of Stimulant Medication on Learning in Children with ADHD" (James Swanson, et al.); and "Social Impact of Stimulant Treatment for Hyperactive Children" (Carol Whalen and Barbara Henker). (PB)