For students to be successful in higher education, compete in 21st century careers and be economically competitive, they will need a greater understanding of mathematics that centers on critical thinking, problem solving, analysis, communication and collaboration (Dean, Hubbell, Pitler, & Stone, 2012; Gasser, 2011; Schornick, 2010). Delivering instruction that focuses on these mathematical skills will require teachers to be proficient at using a variety of teaching practices that will enhance mathematical learning for all students. The purpose of this qualitative exploratory case study was to identify key factors that affected teachers' abilities to make changes to their instructional practices during the implementation of the Common Core State Standards for Mathematics and the CPM (College Preparatory Mathematics) educational program. Eight staff members participated in the case study. Data was collected through the use of 10 interviews and two focus group discussions. Four research questions guided this study: (1) What factors influenced teachers to make changes to their instructional practices during the implementation of the Common Core State Standards for Mathematics (CCSSM)?; (2) What barriers did teachers have to overcome in order to implement changes to their instructional practices?; (3) What supports were needed in order for teachers to implement changes to their instructional practices?; (4) To what extent were teacher's instructional practices and beliefs about teaching impacted by the implementation of the new instructional materials and CCSSM? Eight major findings were identified and included the following: mathematical knowledge, standards, mindset, equity, resources, collaboration, preparation and teacher beliefs. All participants agreed changing one's teaching practices and pedagogies are vital in increasing mathematical achievement of all students, but that change is difficult. The participants believed with the proper supports, knowledge, and growth mindset, it was possible to successfully implement the new teaching materials and mathematical standards. The findings of the study also provide educators with strategies to support teacher growth during the implementation of new educational programs and teaching practices in secondary mathematics. The implications of this study are significant, as all educators must continuously seek to develop teacher capacity in order to increase student learning in mathematics. [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.]