A confluence of circumstances in educational policy and teacher preparation have placed a low priority on elementary science teacher preparation. Historically, a lack of elementary science teachers' subject matter knowledge and pedagogical knowledge has negatively impacted science teaching self-efficacy, which is linked to many teacher and student outcomes. Meanwhile, the past decade has ushered in the Next Generation Science Standards (NGSS) and the modern era of reform-based science teaching. The emergence of self-proclaimed NGSS-aligned resources has outpaced academic examination regarding professional development (PD), curriculum implementation, and curriculum enactment. The purpose of this study was to use social cognitive theory to assess whether the implementation of a phenomena-based science curriculum was related to science teaching self-efficacy and outcome expectations of elementary science teachers. A mixed methods explanatory sequential case selection variant design was used. The initial quantitative strand used the STEBI-A tool to gather information about participants' science teaching self-efficacy and outcome expectancy. A subset of the initial participants was selected for a qualitative interview based on their range of STEBI-A scores. The cases revealed that teachers with higher science teaching self-efficacy and outcome expectancies enjoyed science, prioritized science, and recounted positive student engagement, interest, and motivation more frequently than teachers with lower STEBI-A scores. Teachers involved in a curriculum selection process or those that received coaching sessions from a science coordinator reported developing skills and confidence in teaching science. All teachers reported increased comfort in teaching while using NGSS-aligned curriculum materials over time, but also lacked time to teach science during the school year and referenced their limited experience with professional development. Participants held a wide range of beliefs about the nature of inquiry in science. Teachers' use of science curriculum support materials was varied as well. From a PD standpoint, more time must be apportioned to developing reform-oriented practices in elementary science teachers, and a teacher leadership model could be used to accomplish these goals when contractual time is limited. [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.]