Open Educational Resources (OER) was first introduced in universities as a cost-saving option to traditional textbooks. In 2015, the U.S. Department of Education announced the #GoOpen initiative, challenging school districts nationwide to convert at least one course from traditional curriculum resources to OER. Existing research has focused on the perception of OER's effectiveness, but this study sought to discover whether OER implementation influenced teacher efficacy. The problem addressed in this study was that teacher efficacy in middle school mathematics may be influenced by adequate time, training, and support provided to implement OER effectively. This problem affects classroom teachers, students, and district administration as they transition from traditional curriculum resources to OER. The purpose of this qualitative case study was to explore how the perception of sufficient time, training, and support in implementing Open Educational Resources (OER) influences the efficacy of middle school mathematics teachers. Albert Bandura's self-efficacy theory formed the theoretical framework of this qualitative case study. Middle school mathematics teachers in a suburban school district participated through questionnaires, interviews, and a focus group. Notes and transcripts were analyzed for themes, findings, and implications. This study found that when provided adequate time, training, and support, teachers develop a strong belief in their content knowledge and are more reflective about their teaching. These results may guide administrative decisions on how to support teachers through OER implementation effectively. The study adds to current research and supports future research on the OER phenomenon from the teachers' perspectives. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]