This executive summary discusses the definition of learning disabilities (LD) and how students are identified as having a learning disability. It begins by outlining four major methods that are used to compute the discrepancy-based definition of LD and the flaws of the discrepancy-based model. It then describes an approach to defining LD that is based on how students respond to instructional interventions and how such an assessment process can be developed and used in identification and instruction. The process presented, "responsiveness to intervention," is defined as the change in behavior or performance as a function of an intervention and uses a discrepancy-based approach. However, the discrepancy is between pre- and post-intervention levels of performance. A resistance to intervention approach to eligibility determination identifies students as having a learning disability if their academic performance does not change in response to a validated intervention implemented with integrity. Several models of intervention are presented for adopting the responsiveness to intervention approach in defining LD, including predictor-criterion models that use and teach those skills that best predict reading competency; a dual-discrepancy model based on children's failure to respond to well planned and well implemented general education interventions; and applied behavior analytic models. (CR)