Evaluating and building teacher capacity and agency is critical to ensure that students are exposed to effective teaching strategies with the best possible opportunity for academic success. School districts and teachers are held to high standards when it comes to student outcomes on standardized assessments. As a result, teachers of courses with end-of-course standardized or high stakes assessments are under increased levels of scrutiny because of the impact of these exam results on students, families, districts, and communities. Self-efficacy is a driving force and fulfills a significant role in building teachers' agency and their motivation to accomplish a goal or task. A common element in both educator self-efficacy and effectiveness is introspective reflection on the part of the teacher. This qualitative case study examined the perceived efficacy and effectiveness of teachers of high stakes assessments across various dimensions of teaching to reveal the sources of self-efficacy influencing teacher mindset and growth. Findings revealed that teacher efficacy varies across these dimensions and teachers rely on multiple sources to influence efficacy and inform decision making about their teaching. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]