Due to recent waivers and current expectations of teacher performance, schools have been tasked to close their student achievement gaps in mathematics by 2014. Yet students still have not performed well in mathematics, which may be a direct link to teachers' instructional practices. Identifying a coaching model to improve student achievement and teachers' instructional practices is important to district leaders, school administrators, and teachers. The purpose of this study was to evaluate how a coaching practice with teachers affected student achievement in elementary mathematics. The theoretical foundation of this study was the coaching model, first used by Joyce and Showers, which theorized that teachers who participated in this type of professional development would improve their instructional practices in the classroom, and subsequently, student achievement. A quasi experimental design was employed to test the theory that teachers who were coached would improve student achievement in elementary mathematics. A total of 185 test scores from students were analyzed using an independent measures t test and a repeated measures t test. Findings suggested that the achievement scores of students whose teachers were coached were statistically higher on both state and local assessments. Fourth grade students showed improvement on both the local and state assessments, while 5th and 6th grade students demonstrated significant differences on the local assessments only, but not on the state assessments. This research contributes to positive social change by providing educators with a coaching model that demonstrates how teacher coaching can increase student achievement in elementary mathematics, Grades 4 through 6. [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.]