This study examined teacher and administrator perspectives in regards to the adoption and implementation of an elementary mathematics teaching approach called Cognitively Guided Instruction (CGI), at three elementary school sites of a rural elementary school district, located in the Central Valley of California. A holistic exploratory case study analysis involving teachers and administrators, from each of the three participating school sites and district office, was conducted. The study explores how one elementary school district aimed to improve student learning and began the shift into teaching the Common Core State Standards by adopting and implementing CGI; as it is within the complexity of implementing new innovations there is oftentimes a lack of understanding of effective ways to fully introduce and integrate these improvements. This study seeks to gain a better understanding of teachers' and administrators' perceptions of the adoption and implementation process of Cognitively Guided Instruction. This study uses a combination of theories, including Constructivism, Cognitive Learning and Rogers' Diffusion of Innovation. The study participants are elementary math teachers representing grades one through six, school site principals and one district office representative. The case study design utilized classroom observations, teacher interviews, administrator interviews and a review of documents and materials related to CGI. Research was conducted during the 2013-14 academic school year. The data from these three sources were triangulated and analyzed for emerging categories and subcategories. Six categories emerged from the data: 1) Defining and Understanding CGI, 2) Preparation for Implementing CGI in the Classroom, 3) Professional Development, 4) Using CGI in the Classroom, 5) Institutional and Leadership Support for Adopting, Implementing and Institutionalizing CGI, and 6) Influences on Changing Educational Practices and Teacher and Administrator Beliefs as a Result of Implementing CGI. The findings of the study indicate few differences between the three school sites in regards to their adoption and implementation of CGI: teachers' and administrators' perceptions of the adoption and implementation of the CGI approach was generally positive; teachers felt supported by the school and district leadership, and believed they benefitted from the various training opportunities provided; barriers and challenges identified, possibly had a slowing effect on the process of fully implementing CGI; implications for theory and practice, such as the importance for solid professional development, administrator support, and the recognition that anything new is a process; and the process of adopting and implementing innovations such as CGI progresses through stages. This study concludes with three areas of recommendations: 1) Recommendations for Institutionalizing and Sustaining Cognitively Guided Instruction in the Mountain View Elementary School District, 2) Recommendations for Educational Institutions, and 3) Recommendations for Future Research. [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.]