Co-teaching has increasingly been implemented over the past 20 years as a shared responsibility alternative to more restrictive special education models for providing service to students with disabilities. Results of local school system research in Maryland during this 20-year period are reviewed suggesting that improved special education student performance is associated with increased access to general education classrooms through co-teaching support. System-level co-teaching implementation strategies are identified that result in successful participation by students with disabilities in co-taught general education classrooms and accelerated outcomes on state reading and mathematics assessments. The specific effect of co-teaching as a system-level strategy to close achievement gaps and promote continuous improvement for students with disabilities in Howard County, Maryland, over the past 6 years is described. (Contains 3 figures.)