In the 127th Maine State Legislative Session, "An Act to Implement Certain Recommendations of the Maine Proficiency Education Council" (S.P. 660 -- L.D. 1627) was passed into law as Chapter 489. This amended the chaptered law passed in 2012, "An Act to Prepare Maine People for the Future Economy" (S.P.439 -- L.D.1422), requiring public school districts to implement proficiency-based high school diploma requirements and standards-based education systems. Beginning in 2012, the Maine Legislature's Joint Standing Committee on Education and Cultural Affairs has annually requested that the Maine Education Policy Research Institute's (MEPRI) work plan include empirical research studies designed to compile data, examine progress and explore impacts regarding implementation of this state policy within school districts across the state. This work has furthered the understanding of perceptions in the field and implications of proficiency-based diploma policies within the state, national and global context as well as the implementation in local schools and school administrative units. In 2017-2018, Phase VI of this ongoing research includes two separate research studies examining the impacts of implementing proficiency-based diploma systems within the immediate and wider contexts of public schooling in Maine. One of these studies focused on case studies of high schools to examine the practices, challenges and facilitators as well as the perceptions of high school educators and administrators about meeting the needs of students and their district's requirements for earning a proficiency-based diploma. This report describes the updates to current related literature, methodology and findings from the case study research involving Maine high schools. Findings from this case study research indicate that, as part of the school and district work to implement a proficiency-based system, all case study schools were establishing definitions of proficient, aligning curricula and assessments to common content area standards, and building interventions to remediate with students struggling to demonstrate proficiency. Although specific practices, approaches and perceptions of this work varied among educators and across schools, diligent effort to create a transparent system that benefitted students was evident in all case study schools. Educators and administrators shared that challenges included uncertainty about state-level rules, defining proficient, needing resources to support all students, misalignment with standardized tests, and communication through grading practices. Also, participants in this study indicated that transition to a proficiency-based education system could raise expectations for lower performing students, offer greater professional collaboration, and provide more clarity regarding academic standards.