This study examined the implementation of seven co-teaching strategies as self-reported by experienced middle and secondary mentor teachers in a large suburban school district. Seven case studies, three middle school and four high school mentor teachers, were analyzed. Findings reveal that mentor teachers supported the use of co-teaching in teacher preparation programs. However, mentors did not always implement the co-teaching strategy they identified as the best strategy for supporting P-12 student learning. Implementation decisions were based upon a number of factors: limited time in co-planning, limited training on co-teaching in specific content areas, and limited ongoing professional development. This study will inform teacher education programs considering co-teaching as a model for secondary and middle preservice teacher clinical experiences and share findings that outline components necessary to support mentors and preservice teachers utilizing co-teaching to enhance learning for all stakeholders.