The underrepresentation of Black girls in high school STEM courses is a pressing issue reflecting broader societal inequities and diminishes the potential for innovation in science, technology, engineering, and mathematics. The problem of low enrollments of Black girls in high school STEM classrooms impacts not only the educational outcomes for Black female students but also the diversity and inclusivity of STEM fields at large. The purpose of this qualitative exploratory multiple case study aimed to explore STEM teachers' perceptions of their roles in encouraging and supporting Black girls in STEM education. The ecological systems theory guided the research, which considers the multiple environmental systems influencing an individual's development and emphasizes the importance of various social contexts in shaping educational experiences. The study employed a multiple case study with invited and gathered data from twenty high school STEM teachers in Southeastern Pennsylvania, USA, and Ghana, Africa, through online surveys; nine of those high school STEM teachers participated in semi-structured online interviews. The analysis involved coding the data to identify themes related to the research questions, which aimed to uncover how teachers perceive their influence on the encouragement and support of Black girls in their STEM courses and identify the barriers their students face. The results revealed a consensus among teachers on the importance of culturally responsive teaching and creating inclusive learning environments. Teachers acknowledged significant barriers, including societal stereotypes and a lack of resources, which hinder Black girls' engagement and success in STEM. Furthermore, the findings highlighted the necessity for ongoing professional development to equip teachers with the skills to support Black girls effectively. The study concludes addressing the underrepresentation of Black girls in STEM requires systemic changes across educational, community, and policy levels to foster an inclusive and supportive educational environment. Future research should continue to explore the long-term effects of these interventions and expand the scope of studies to include different educational settings and comparative analyses between diverse geographical locations. Recommendations for practice include implementing comprehensive professional development programs and curricular adjustments to better reflect students' diverse backgrounds. [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.]