The current study examined the effectiveness of blended learning systems in a selected group of five elementary schools in one school district. It analyzed the influence of on-site leadership and teacher professional development on the implementation of blended learning and its influence on student engagement. Although blended learning integrates different teaching methods based on multiple theories, such as Cognitivism, Constructivism and Behaviorism, this study adopted a guiding theory based primarily on Cognitivism. A qualitative approach with a multiple-case study design was employed. The qualitative data was collected through a semi-structured interview protocol, and individual interviews took place via Zoom with the participants, which included elementary teachers and principals. The findings respective to the first research question revealed that principals and teachers perceived explicit teacher professional development on blended learning as the most effective teacher professional development influencing student engagement. With respect to the second research question collaborative leadership yielded effective leadership and, in turn, influenced the implementation of blended learning. The most significant implication of this study was that blended learning influenced student engagement. Teachers reported more participation, increased participation, and more student engagement with blended learning systems. Principals commented that students were engaged and that this involvement helped with resolving behavioral issues. [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.]