There is a lack of implementation of instructional strategies to assist middle school teachers in improving mathematics education for their students. Coaching is one solution to this problem, but its impact on student achievement is unclear. This case study evaluated the relationship between coaching and teacher efficacy and the impact of these constructs on mathematics student achievement at a charter school in the southern United States. The study was based on the theory of instructional coaching as a model for teachers' professional development. A dependent samples "t" test was used to analyze district quarterly mathematics data from the Northwest Education Association Measure of Academic Progress (NWEA MAP) during the implementation of coached strategies. The analysis indicated a significant increase in mathematics achievement from 3rd to 4th quarter for 400 students in grades five through eight, "t"(399) = -4.011, p =0.028. Surveys, journals, and interviews were also used to determine how coaching recommendations were implemented, the degree of teacher support received, and perceptions among teachers and the coach. A line-by-line analysis of participants' responses was conducted, leading to the disclosure of themes that were used to determine efficacy of the program. The major findings were the need to develop the role of the coach; increase teacher learning through observation; schedule sufficient time for teachers and the coach to collaborate on student learning; and work to improve teacher self-efficacy. This study could contribute to positive social change by demonstrating how coaches can assist educators in changing mathematical teaching strategies to align with students' needs in the 21st century to appropriately educate students for life in a technological world facing major and continuing challenges. [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.]