When school districts do not have established policies to guide training, practice and professional development for all co-teaching staff, inconsistencies and inequities may arise for the student populations most directly impacted by the lack of those policies, including both general and special education students. In order to best serve the students of all abilities that populate co-taught classes, it is necessary to establish a culture of inclusion that is founded upon research-based models and practices, along with built-in training and support for co-teachers that will provide the most effective learning environment for the students and the most positive working environment for the co-teachers. Co-teaching (or collaborative teaching) requires the coordinated efforts of at least two teachers, typically one general education and one special education, who share their expertise and skills in order to teach a class with students of all abilities (Bauwens & Hourcade, 1997b). This research identified the current state of co-teaching training, practices and support at a large suburban high school district in the Midwest of the United States, referred to as Sample High School throughout this study. In order to accomplish this research, a qualitative study was performed using a Google form survey, which consisted of questions that gathered data from the co-teachers within the district, and interviews with eight building and district administrators, in order to identify current training and support practices for co-teaching. The culturally sustaining pedagogy described by Waitoller and Thorius (2016) was used to analyze the findings from this study, in order to support a sustainable culture of inclusion in practice. The results from both the co-teacher surveys and the administrator interviews revealed gaps in communication and understanding of co-teaching practices in the district, identified the lack of formality in regards to co-teaching team formation, training and professional development, showed impacts from the 2020-2021 pandemic school year restrictions and acknowledged a desire to improve current practices. Based on these findings, several implications for improvements to the district's current practices, including the establishment of a clear co-teaching mission and vision, improving the reputation of co-taught classes and establishing leveled co-teacher training and in-district professional development were suggested, in order to maintain a sustainable culture of inclusion in practice within the district. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]