This descriptive, qualitative case study investigated how three high school teachers in non-STEM subject areas developed integrated STEM (iSTEM) pedagogies for conventional classroom lessons in a high-technology makerspace. The school in focus adopted a STEM teaching policy that required all teachers to implement iSTEM teaching in the school's makerspace called the Innovation Center. However, pre-study, needs-assessment data revealed that many staff teachers viewed iSTEM teaching in the Innovation Center as a somewhat unrealistic expectation for literature-supported reasons that included a lack of professional and teacher candidacy training for iSTEM, ambiguity in defining iSTEM literacy, daily demands of meeting a standardized curriculum, unfamiliarity with teaching in a makerspace, and an ambiguity regarding STEM policy learning initiatives. The study group of teachers underwent a targeted professional development program, and afterward, they taught their own self-described iSTEM lesson in the Innovation Center. Data collection included interviewing and observations. The study's findings revealed that iSTEM makerspace education offers significant, positive affordances for teachers, including curriculum renewal, an impetus to take risks, and a clearer vision of iSTEM teaching. However, teachers also reported that to overcome barriers to iSTEM makerspace teaching, they need support that addresses time management issues and daily scheduling, meaningful professional development, and clear lesson exemplars of iSTEM that work within their classroom structures. This research will provide insights into some practical instructional approaches educators can take when introducing iSTEM makerspace learning into their classrooms. [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.]