This sequential explanatory mixed methods study explores elementary mathematics teachers' perceptions regarding their mathematical self-efficacy, how teachers describe their perceptions about their prior mathematical learning experiences and their impact on their instructional practice in the elementary mathematics classroom. In support of this purpose, it is essential also to examine school leaders' role in developing elementary teachers' mathematics self-efficacy. The quantitative data was collected using the Mathematics Teaching and Mathematics Self-Efficacy Scale (MTMSE) online survey. A total of 60 elementary teachers in Grades 3, 4, and 5 were analyzed by descriptive statistics and correlations. A focus group of 6 elementary teachers was conducted, and analysis was explored to provide a more in-depth understanding of the quantitative results about teachers' prior experiences, beliefs, attitudes, and confidence levels around elementary mathematics. The last part of qualitative data collection and analysis was from eight individual campus administrator interviews. These interviews explored how support by campus administrators can increase elementary mathematics teachers' self-efficacy. From the teacher focus group and administrator individual interviews, it is clear that with experience and the correct level of support, teachers' levels of self-efficacy are increased. Experience and available support were shown to positively impact the self-efficacy of elementary mathematics teachers, according to the findings. The data indicated that as elementary mathematics teachers accumulate experience and utilize collaborative support to expand their knowledge of mathematical concepts and ideas, they experience a gradual surge in self-confidence and a heightened sense of assurance when instructing mathematics to their students. [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.]