A Response to Intervention (RTI) model proposes identification of students with reading difficulties on the basis of a series of progressively more intensive instructional interventions over extended periods of time. Learners with serious reading difficulties are those whose difficulties are not resolved by the interventions. Three advantages of an RTI approach include that children need not wait to fail (Vaughn & Fuchs, 2003) to be eligible for support, RTI avoids problems associated with process-deficit and discrepancy models, and RTI is instructionally grounded, enhancing the ecological validity of the diagnostic process and more clearly grounding it in subsequent instruction. Although everyone views RTI as a generally positive step toward a more transactional perspective, the authors view that many RTI approaches do not go far enough in acknowledging chronic problems in their efforts to define and to respond to severe reading difficulties. RTI approaches may even undermine rather than support the literacy learning of students. To explain their perspective, this essay consists of four parts. In the first part they consider views of deficit, difference, and variability that have played important roles in the thinking of both special educators and literacy educators during the previous 30 years. In the second part, they explore pedagogical implications of a natural-variability model of reading that is central to our thinking. In the third part, they explore what a perspective based on natural variability suggests about teacher education and broader issues related to implementing RTI. The final section of the essay presents conclusions and highlights some connecting themes across the four articles that make up this NDR collection. (Contains 2 figures.)