The relatively new utilization of learning management system (LMS) facilitated blended learning in secondary public schools has grown in popularity, but there is a void in research at this level. Teachers learned how to use the LMS features and honed their blended learning design skills through their own experiences, and in observation of their students' experiences. In this study, the knowledge teachers built and the decisions they made while designing blended learning were explored. In this mixed-methods study, the quantitative and qualitative results aligned, indicating that teachers design courses using a variety of components, often in different ways. Six themes emerged. The relationships between themes were used to create a theoretical visual of the factors impacting secondary teachers' decisions in the design of LMS-facilitated blended learning. Teacher design decisions were focused on the impact their choices would have on students. Variation in course design was purposely used by teachers to differentiate for students individually; however, variation was also the result of design challenges blocking teachers from a specific design choice. The implications for practice primarily focus on removing the design challenges. The results of this study add to other foundational studies to begin to fill the research gap in the area of LMS-facilitated blended learning design in secondary schools. [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.]