This study was designed to examine the lack of ongoing evidence-based preparation models used by co-teachers to plan lessons and assessments for students with special needs within inclusive classroom environments. Co-planning is especially important when general and special education teachers are working together to support students with disabilities. The purpose of this qualitative case study was to explore inclusive planning contexts that public-school teachers report as required to educate diverse learners, and also to explore needed professional development on teacher planning. The participants were 12 urban inclusive classroom teachers, six special educators and six general educators. The study results were revealed through phone interviews and observations of teacher planning during a design and develop professional development activity purposed to address the research questions. This study incorporated a 6-step process using thematic data analysis. The inclusive classroom teachers planned or modified lessons and assessments together but reported that they frequently had to plan outside of preparatory periods due to limited time during the school day. The co-teachers reported that they benefited from different planning approaches such as multi-cultural learning, Universal Designed Learning, and multiple tiers of supports and services. The co-teachers did not report a focus on inclusive classroom professional development or on co-teacher leadership. These concepts are needed aspects of professional development. The co-teachers operated from a systems approach of co-planning daily classroom accommodations, modifications, tier supports, and from a multicultural focus in evidence-based inclusive settings. This study could inform educators who seek direction in inclusive co-planning practices, to help the educators increase meaningful educational support for diverse learners. The study results are consistent with a theoretical framework that combines John Dewey's concepts of constructed learning designs and systems leadership theories of Kenneth Leithwood and Peter Senge. Co-planning improvements suggested by the participants focused on the adequate distribution of teaching tasks and distributed leadership. Future research should focus on teacher collaboration and the integration co-planning professional development. [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.]