With respect to co-teaching, there is a lack of empirical research at the high school level. Furthermore, few researchers have considered asking high school co-teachers to share their beliefs and perceptions about what makes co-teaching a successful model. To fulfill both the needs of students who are educated in co-taught classrooms and the lofty requirements of federal legislation, the perceptions of high school co-teachers needed further investigation. This study took aim at reducing this gap in the existing literature by adding substantial data via the voices of high school co-teachers. High school co-teachers in the states of Alabama, Georgia, Louisiana, Mississippi, and Texas were queried on their perceptions of successful co-teaching. This study was conducted via a quantitative research approach with a descriptive design. The descriptive research design that was utilized was sample survey research. A total of 126 co-teachers (n = 126) actually completed the survey and had their responses included in the study's results. Participants included 53 general education co-teachers (certified teachers of Math, Science, Social Studies, or English Language Arts) and 73 special education co-teachers (certified teachers of students with disabilities). Data were collected and analyzed using methods associated with quantitative (e.g., inferential analyses) and qualitative (i.e., coding schemes) research practices. What was learned from their voices, via their survey responses, can help high schools successfully implement and improve this instructional model. [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.]