The philosophy behind the Common Core State Standards (CCSS) and its tenets of critical thought, creativity, and application of knowledge require a shift from a focus on content knowledge to how that knowledge is applied across the curriculum and why it forms the foundation of education. The problem now facing educators is that CCSS has changed expectations for students without providing adequate professional development (PD) to ensure the proper adjustment to instructional strategies to meet its requirements. The purpose of this quantitative study is to determine how teachers have adjusted their application of instructional strategies to target Common Core learning objectives in high school classrooms and to provide recommendations on how site and district administrators can better structure PD to facilitate teacher needs as they shift their instructional practices. Through quantitative survey data from high school teachers and administrators, the study was able to determine that, while education has seen a shift since the adoption of the CCSS, it has not necessarily translated into a shift of instruction throughout all classrooms. In addition, the majority of teachers indicate that the current structure of professional development they receive within their district, at their site, or from out-of-district training has had only limited impact on their instruction to meet the needs of the CCSS. This research indicates that teachers want to professionally learn from teacher-experts in a collaborative setting. To adjust instruction, teachers must first be knowledgeable about what they are being asked to teach, so they can design strategies for students to learn. Almost 97% of the teachers in this study claimed to have at least some knowledge of the CCSS; however, of the 97% almost 40% did not feel they had a good grasp of those standards, let alone expertise. There is a need, as indicated by the results of this study, to focus on both increasing the knowledge base of teachers and administrators on the CCSS and structuring PD in such a way that teachers can continue to grow as learners, meeting the needs of their students by adjusting instruction to meet the demands of the 21st century. [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.]