With the 2015 change in science standards to align more closely with the Next Generation Science Standards, as the district STEM coach, I saw a need for professional development that addressed the lack of understanding and skill needed to teach the Science and Engineering Practices, specifically the practice of Scientific Augmentation. This mixed-methods action research study aimed to investigate the impact of professional development and coaching on 4th-6th grade science teachers' pedagogical content knowledge (PCK) of scientific argumentation and their self-efficacy to teach scientific argumentation. Data collection consisted of (a) PCK of Argumentation Assessment, (b) PRIME PCK Rubric and observation notes, (c) Science Teaching Efficacy Belief Instrument -- Form A, (d) coaching notes, (e) response from open-ended reflections, and (f) personal coaching reflections. Triangulation of data suggests that three days of professional development and a coaching cycle over eight weeks strongly impacted participants' PCK and self-efficacy in their ability to teach students to engage in scientific argumentation. Participants grew in the skills of using evidence and supporting student interactions throughout the research intervention. Through closer qualitative analysis, participants' self-efficacy increased most due to mastery experiences during professional development and coaching sessions. This research suggests that repeated professional development sessions combined with coaching cycles can increase teachers' PCK of argumentation and science teaching self-efficacy. [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.]