Children and youth exhibiting serious emotional, behavioral, and interpersonal problems create substantial challenges for schools, teachers, their parents, and other students. Stu-dents having these characteristics are often underserved or unserved by educational and mental health systems in the United States. Recent prevalence rates for children served as emotionally disturbed (ED) under the Individuals With Disabilities Education Act is less than 1 percent although over 20 percent of the school population could qualify for a psychiatric diagnosis. A major reason for the underservice of children as ED lies in the federal definition of emotional disturbance which is nebulous, often illogical, and self-contradictory. An alternative approach to ED identification based on a student's response to an evidence-based intervention is proposed in this article. Response to intervention is defined and described along with methods and procedures for quantifying whether or not a student shows an adequate or inadequate response to an evidence-based intervention implemented with integrity.