Background/Context: Teacher collaboration, instructional practices, and efficacy are linked in various ways in the literature. For example, in schools where teachers reported greater use of differentiated instruction, team collaboration and culture were reportedly higher (Smit & Humpert, 2012). Further, teachers' instructional mastery experiences lead to higher efficacy (Tschannen-Moran & McMaster, 2009). Tomlinson (1995) suggests that getting teachers to continue using differentiated instruction requires those teachers to experience quick success (i.e., mastery experiences that lead to increased efficacy). Bruce, Esmonde, Ross, Dookie, and Beatty (2010) found that teachers with high efficacy were more likely to try challenging instructional approaches that required taking risks in their classrooms and to use assessments. Based on our literature review, we hypothesized that teachers' reports of their collaborative practices would be related to their teaching efficacy when mediated by their reported differentiated instruction use. Purpose: The purpose of this study was to examine connections between teachers' perceptions of their collaboration, their reported use of differentiated instruction (a particular instructional practice), and teacher efficacy in high-poverty rural schools in a Midwestern state. Participants: Survey, demographic, and assessment data were collected for 95 elementary schools, 1,623 elementary teachers, and 4,167 students in rural high-poverty areas located in the northern regions of a Midwestern state. Research Design: Data from the first year of a large-scale, longitudinal randomized control trial designed to evaluate the effects of a leadership training program were used for this study. Data Collection and Analysis: Survey data containing collaboration, differentiated instruction, and teacher efficacy scales were collected from teachers during regularly scheduled faculty meetings. Demographic and achievement data were collected from a state accountability data system. We employed multilevel structural equation modeling (MSEM) to analyze our data, allowing us to take into account the nested structure of the data (i.e., teachers' responses nested within schools). Results: After controlling for school- and student-level characteristics, we found positive, statistically significant connections between teacher collaboration and teachers' reports that they differentiated instruction (ß = 0.43, p<0.001) and between differentiated instruction and teacher efficacy (ß = 0.38, p<0.001). Conclusions: The results are potentially significant for researchers and practitioners interested in approaches to improving teacher practices and strengthening efficacy beliefs. Our outcomes demonstrate the importance of teachers' collaborative work around school improvement, curriculum and instruction, and professional development. Further, our work extends what is known about sources of teacher efficacy. Theoretically, via mastery experiences gained through collaboration and reports of using differentiated instruction in their classrooms, teachers' efficacy beliefs were strengthened. In sum, district and school leaders, as well as policy makers, should recognize the kinds of supports that teachers need to improve instruction.