These retrospective case studies used a qualitative approach to examine how three mid-west high schools implemented RTI programs in order to raise the achievement of students with disabilities. The study examined two high schools that met Adequate Yearly Progress (AYP) for their measurable subgroup of students with disabilities. A third high school that did not meet AYP was employed as a counter case. The study used staff surveys, teacher focus groups, and administrator interviews to determine common elements of the school cultures for handling conflict and resolving differences. Common elements of professional development were also found to move staff toward meeting AYP for their students with disabilities. In addition, it was learned that the use of Professional Learning Communities (PLC's) provided a third approach for implementing RTI. Through PLC's, the process for determining both the specific types of interventions and the subsequent provision of interventions happened at the classroom level. The study provides timely information for high schools embarking on the implementation of a RTI program as it highlights the central role that special education teachers play in developing and delivering interventions. Although the study size is limited to three high schools, further study of high schools using the PLC process to raise the achievement of students with disabilities would generalize the use of PLC's as a third approach to RTI. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]