The research aimed to provide a complete understanding of characteristics, facilitators, and challenges in implementing professional learning communities in multi-age schools. This study utilized a mixed-methods multiple case study design. Participants in this study were teachers from two private K-8 multi-age schools. The characteristics of professional learning communities and their influence on school quality and student performance were identified. Results confirmed that experiences in professional learning communities increased teacher involvement in all six domains, especially in collective responsibility, reflective dialogue, and peer collaboration. Results indicated that professional learning communities explained significant variance in teacher-perceived school quality measured by academic expectations, communication, and engagement. The sustainability of a successful professional learning community is vital to school quality. The insight gained from this study revealed several factors that enhance the development of professional learning communities in multi-age schools. The first theme, school structural conditions, included subcategories such as time, space, technology and instructional materials, communication systems, district support, and school size as facilitators of professional learning communities in multi-age schools. The second theme, school human and social resources included parental involvement and support, openness to innovation/improvement, professional development, and supportive and caring relationships between students and teachers. The third theme was shared and supportive leadership which included the roles of principal and teacher leader role. Results from this study demonstrated that lack of time, technology, supplies, instructional materials, and parent support were the top challenges in teaching and implementing professional learning communities in multi-age schools. This study offered suggestions for school leaders looking to make practical and authentic changes to improve professional development during school transformation. [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.]