Responsiveness-to-intervention (RTI) is the front-running candidate to replace current practice in diagnosing learning disabilities, but researchers have identified several questions about implementation. Specific questions include: Are there validated intervention models? Are there adequately trained personnel? What leadership is needed? When does due process protection begin? and Is RTI a defensible endpoint in the identification process? These questions were addressed by examining four existing large-scale RTI models, Heartland Model (Iowa), Intervention-Based Assessment (Ohio), Instructional Support Teams (Pennsylvania), and the Problem-Solving Model in Minneapolis (Minnesota) Public Schools. The RTI process led to positive outcomes for children with and without disabilities, but all four models were phased-in over time, relied on extensive training for a multidisciplinary team, and followed a protocol to develop data-based adaptations. Clarification about team membership, leadership, and initiation of due process is still required. Additional questions about RTI were generated regarding students in secondary grades, parental involvement, and fidelity of implementing. Recommendations for implementation are included. (Contains 2 tables.)