MCL unclearly defined for the teachers asked to implement it in the classroom. This study sought to determine how teacher's implement MCL through the data collection of a mind map, which instructional components teachers used, the ideas that MCL has advanced and the idea that MCL made sense of. This qualitative case study analyzed six teacher's interpretations of how they implement Mass Customized Learning (MCL) in classrooms. The participants provided teacher created mind maps, interviews and lesson plans. The data was analyzed as "mini cases" using thematic coding. The overall analysis developed themes from the gathered data of mind maps, interviews and lesson plans. There were six themes that can be used to help answer the research questions: diverse by design, learner-centered, options, instruction, what does not fit, and trial and error. The results from the analysis developed six themes related to how teachers' implement MCL in the classroom. Diverse by design and learner centered help to establish how learning is student-centered. The themes of options, instruction, what does not fit, and trial and error highlight the means that teachers to use to construct instruction in an MCL classroom. These themes work here to provide an uncommon picture of MCL. This study helps to expand the body of knowledge but leaves room for future research in secondary MCL implementation. [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.]