This action research study examined the implementation and impact of a job-embedded professional development intervention that included professional learning community (PLC) sessions and individualized feedback and coaching. Participants in the study were eight high school teachers who had historically demonstrated poor classroom performance and were selected by the school's leadership team to participate in the professional development intervention. The study examined the implementation process, changes in teacher efficacy before and after the intervention, use of formative feedback and coaching to change teaching behaviors, and the perceptions of teachers about the intensive professional development and coaching activities. Quantitative measures were the Teachers' Sense of Efficacy Scale (TSES) and Teacher Advancement Program (TAP) rubrics. Minutes from the PLC focus sessions, Individual Growth Plan journals, individual interviews, and the researcher's journal were the qualitative data sources. Triangulation of the data suggested that for seven of the eight participants, teacher efficacy increased, and for six of the eight participants, teaching practices improved by the end of the intervention. Quantitatively, the average scores of the eight participants collectively increased by 0.53 points on the TSES and 0.29 points on the TAP rubrics. Analysis of the quantitative data also indicated that the greatest improvement was in the area of classroom management. Analysis of qualitative data rendered results and findings that explained teachers' perceptions and beliefs regarding how a job-embedded professional develop intervention impacts teacher efficacy and teaching practices. Participants' perceptions and beliefs indicated that increases in their efficacy scores and improved classroom performance are likely to happen when teachers feel more confident and competent, are provided with quality mentors and effective coaching, are reflective practitioners, and are provided with professional development that is relevant to their needs and the needs of 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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]