The goal of this mixed methods study was to examine educator and student perceptions of the implementation of social-emotional learning (SEL) and the RULER (i.e., recognizing, understanding, labeling, expressing, and regulating) approach in a Catholic school. The study investigated the perceptions of teachers, staff, and students about the implementation of SEL and RULER across elementary and middle school grade levels. The RULER approach is a K-12 SEL initiative designed to build the emotional intelligence and social-emotional competencies of all members of a school community. Data were gathered over a 4-month period through interviews with teachers and students, an educator survey, document analysis, and classroom and campus walkthroughs. The study produced findings around SEL and RULER implementation. The findings suggested SEL and RULER was valued by educators but there are challenges to implementation that may be obviated if the implementation team has a thorough understanding of the process of implementation of an initiative. Recommendations are provided to public and Catholic elementary and middle school leaders and SEL and RULER developers. [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.]