Over the past three decades, researchers have found cooperative learning to have positive effects on student achievement in various subject areas and levels in education. However, there are limited studies on the impact of cooperative learning on student achievement in the area of high school mathematics. This study examined the impact of cooperative learning on student achievement and the impact of cooperative learning on professional development on teachers' plans for instruction in a Chicago suburban Advanced Algebra and Trigonometry high school mathematics classroom. The samples studied consisted of three mathematics teachers, 164 junior level students in 2014-2015 and 120 junior levels students in 2015-2016. The impact of cooperative learning was measured through a quasi-experimental mixed-methods design. Student achievement was measured by the means of the final exam and the mathematics portion of the ACT. Professional development data was analyzed through an analysis of teacher interviews conducted by the researcher. The data analysis indicated that the incorporation of cooperative learning decreased students' scores in the areas of the final exam and the ACT at a statistically significant level. The study also revealed that a cooperative learning pedagogy does impact teachers' plans for instruction in an Advanced Algebra and Trigonometry high school mathematics classroom. [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.]