The Least Restrictive Environment (LRE) component of IDEIA 2004, NCLB requirements, and research indicating increased achievement for students with disabilities in the general education environment, have led to the inclusion of students with disabilities into the general education classroom and the use of co-teaching model is increasing throughout the United States. Research indicates that, for inclusion to be successful, administrators and general education teachers need to receive adequate training in special education, supports, and resources to implement successful integration and inclusion of students with disabilities in the general education setting (Ainscow, 2000; Burton & Pace, 2009; Cox, 2008; Praisner, 2003; Villa, Thousand, Meyers, & Nevin, 1996). Co- teaching has shown to be an effective model of inclusion that can support the requirements of NCLB and IDEIA (Bryant-Davis, Dieker, Pearl, & Kirkpatrick, 2012; Friend, 2008; Villa et al., 1996). The purpose of this single case study was to determine the fundamental attitudes, practices, relationships, structures, programs, and supports that contribute to successful co-teaching partnerships in a high school setting. This study used a survey, classroom observations, and semi-structured interviews to gather data to determine what characteristics contribute to successful co-teaching. This case study utilized purposeful case sampling. Participants were chosen from one of the highest performing high schools in a large urban school district in Southern California. The research showed that small schools that incorporate small group work with consistently scheduled meetings for collaboration foster community and contributes to the success of co-teaching. Curriculum that lends itself to small group work is a factor in successful co-teaching. Additionally, having adequate materials, supplies, and access to the latest technology supports successful co-teaching program. Furthermore, special educators staying with students for 4 years was found to be beneficial for both general and special education students and co-teaching partnerships. Experience and time in a co-teaching partnership was shown to be a factor in the success of the co-teaching model. Overall, the co-teachers attitudes were positive and the research showed that all of the teachers worked well together, had respect for the special educators, and all but one felt that co-teaching had improved their teaching practice. Respect and trust were shown to be the most important aspects for a successful co-teaching partnership. Similar to the research for the past 40 years, all the co-teachers requested more training on co-teaching and the general educators wanted more training on special education strategies and co-teaching.