Elementary teachers are generalists, usually with a reading background. As such, a number of teachers have low self-efficacy about teaching mathematics for conceptual understanding. Researchers suggest that some major categories associated with this problem are not enough adequate professional development (PD) addressing conceptual understanding in mathematics teaching (Carney et al., 2016; Taton, 2015), teachers using procedures similar to how they were taught as students (Yao et al., 2021), and teacher preparation programs failing to address low self-efficacy in mathematics teaching with their pre-service teachers (Briley, 2012; Ozben & Kilicoglu, 2021). The purpose of this study was to determine if a sustained, active content-based professional development program would increase the mathematical self-efficacy of elementary math teachers. Through this quantitative, non-experimental survey design, I formally investigated this problem by analyzing results from a pre-and post-self-efficacy survey using a modified MTEBI with 231 elementary math teachers from a north central Texas school district to determine their beliefs about teaching math conceptually. I further stratified the teachers by grade level bands, years of experience, and whether they were alternatively or traditionally trained and certified to discover any differences in self-efficacy gains. Using quantitative statistical tests of paired-samples t-tests, independent-samples t-tests, and ANOVA tests, the data were analyzed and found statistically significant differences in self-efficacy gains overall, for concepts presented during the professional learning program, and for concepts not presented in the program. There were statistically significant differences in self-efficacy gains between K-2 and 3-5 teachers with the upper-grade teachers increasing their self-efficacy scores more than the lower-grade level teachers. There were no statistically significant differences between teachers with varying years of experience, but there were differences in the PD concepts between alternatively and traditionally trained teachers with alternatively trained teachers making the biggest gains. The data showed a relevant, sustained PD program can be effective in increasing math teachers' self-efficacy in conceptual understanding of computational strategies. [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.]