To foster proper educational growth and to ensure equal scholastic opportunities for students in Kindergarten through twelfth grade (K-12) in the United States of America, the state governors and chief school officers established the Common Core State Standards (CCSS). Teachers being at the forefront in realizing the goals of these standards, necessitated the move to investigate the importance of teacher readiness for the proper implementation of the CCSS. The problem was teachers in K-12 in the United States lack the readiness to implement the CCSS because they have not received proper training. With improper training, teachers would not possess the appropriate knowledge to execute these standards, which would affect the students' future career and college readiness. Hence, the study explored the perceptions of K-12 teachers in the United States on how to improve teacher readiness through training. The theory of self-efficacy was the foundational framework employed to address the teacher readiness and implementation of these standards. Using qualitative multiple case study, the researcher interviewed ten teachers from New York State. The interview, focused on the two research questions, which centered on what the teachers need to learn through training and the type of training they need to implement the standards properly. Data collection involved interviewing ten teachers on ten questions through video (Zoom) and audio (phone). Eleven themes and two subthemes emerged from the data analysis with the help of NVivo 12 and manual approach. The findings from the analysis illustrated teachers lack training in various classroom activities that would assist them in implementing the CCSS, and they have not had the types of professional development they need to implement the standards properly. These findings warranted recommendations for practice for school administrators and educators. There were suggestions for further research on this topic. [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.]