The current study examined the effects of a co-teacher professional development course for increasing the knowledge and self-efficacy of special education and general education geometry teachers in an inclusion setting. The professional development course included instruction on Universal Design for Learning instructional strategies as well as similarity and congruence in geometry. The course was presented in a blended learning format and included in-person and online activities. The online activities used animated scripts of teacher instruction for collaborative discussion and decision-making. A multiple probe design across three sets of two teachers for a total of 6 participants was used in this study to demonstrate a functional relationship between the independent and dependent variables. The participants were six special education and general education geometry teachers from public charter schools in Washington, DC. Results of the study demonstrated that participants were able to improve their content and pedagogical content knowledge in geometry as well as their self-efficacy for teaching in an inclusion setting. Specifically, special education teachers demonstrated a greater increase in content knowledge while general education teachers demonstrated a greater increase in self-efficacy for teaching students with disabilities. The study suggests that providing professional development for co-teachers can enhance collaboration as well as increase content knowledge and teacher self-efficacy.