The Arkansas Department of Education Co-teaching Project was designed to assist Arkansas schools in the implementation of more inclusive service delivery models for students with disabilities. The project began due to a need to increase the number of students being served in less restrictive environments, but evolved into a systematic statewide program that has impacted both service delivery as well as general and special education teacher practice. Support for the systemic change project was provided annually through a comprehensive professional development model including face-to-face and online professional development, technical assistance, informational resources, and ongoing evaluation. This article provides the details of the systemic change occurring over a five-year period through a comprehensive evaluation model. Participants in the project included five cohorts, 143 school districts, 208 schools, 789 teachers and 3920 students. The results of the comprehensive evaluation plan indicate, over time, increases in the implementation of building-level supports, rated performance of co-teaching partnerships and grades for students with disabilities in co-taught classrooms. The evolution of the model extended to include web resources, interactive webinars, onsite coaching and specific evaluation feedback and recommendations to individual schools and teachers. This comprehensive approach to professional development was considered critical to the overall changes in state, district and classroom-based practices. (Contains 5 tables.)