The purpose of this systematic grounded theory study was to explain how problems inherent in co-teaching relationships are resolved by secondary school special education and general education teachers at an urban school district in Eastern Iowa. The participants were general and special education secondary school teachers involved in effective co-teaching partnerships. Data was collected from five partnerships, utilizing focus groups, interpersonal behavior theory questionnaires, classroom observations, and individual interviews. The researcher analyzed the data using systematic grounded theory procedures of open coding, axial coding, and selective coding to develop a theory grounded in the data collected about the process by which teachers overcome problems in co-teaching. The theory, Achieving Symbiosis, reflects three main stages of this process. In Initiation, a co-teaching relationship begins. Then, teachers work at becoming effective in the Symbiosis Spin. Finally, Fulfillment is achieved when all the pieces fit together to create an effecting co-teaching partnership. The theory is presented as a hypothesis for future research to explore later. Insight gained from this study supports co-teachers as they work through the process of creating effective co-teaching partnerships, as well as administrators who support co-teachers in their buildings. [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/en-US/products/dissertations/individuals.shtml.]