Calls to strengthen and diversify our nation's STEM workforce outline the need for expansion and improvement of STEM learning opportunities made available to students from minoritized backgrounds. As broader systemic issues of educational inequity disproportionately exclude students from minoritized backgrounds from high-quality STEM learning environments, recruitment and retention of STEM teachers trained in antiracist and socially just (ARSJ) teaching practices is vital. Because traditional STEM teacher education models often separate university from K-12 schooling contexts, university explorations of evidence-based and progressive views of STEM teaching and learning rarely make their way into beginning teachers' repertoires. Furthermore, as pre-service teachers become teachers of record, university supports (e.g., observational feedback, co-planning) often diminish. Thus, learning ARSJ STEM teaching practices requires reimagining traditional teacher education models. Despite such needs, little is known about how pre-service and beginning in-service STEM teachers learn to teach towards ARSJ aims. This begs the question, how might a unique reform model of teacher education serve to achieve this goal? This dissertation studies teacher learning within a case of a unique reform model of teacher education through extended, embedded, and placed-based supports called The Teaching School (TTS). Throughout the study, I explore four student teachers and beginning in-service STEM teachers' experiences learning ARSJ teaching practices in a pandemic-induced virtual school year. I approach this work through a lens of critical sociocultural learning theory and a framework of seven ARSJ STEM teaching practices. Throughout the 2020-2021 academic year, I followed two student teachers and two beginning in-service STEM teachers' engagement in and uptake of opportunities to learn ARSJ STEM teaching practices made available through TTS. Making use of design-based ethnographic research methods, I collected over 10 hours of interview data, more than 110 hours of classroom recordings, 139 field notes, and 38 journal entries. I used constant comparative analysis to identify patterns among and across participants and over time. Across the data, I found distinct differences in participants' commitments to improve on practice and understandings of ARSJ STEM teaching practices, shaping the ways participants engaged in and took up opportunities to learn ARSJ STEM teaching practices. Data related to school culture and mentors suggested that although school community members were dedicated to ARSJ STEM teaching practices, perceptions and approaches to practice varied. Participants' experiences within school culture shaped how they learned about and attempted to enact ARSJ STEM teaching practices, with interactions with mentors who were more aligned with ARSJ STEM teaching practices producing higher and more effective engagement with learning opportunities. Although all participants displayed commitments to learning ARSJ STEM teaching practices, commitments to improvement on practice, or knowledge of how to improve, varied. Participants who were more successful at learning to integrate ARSJ STEM teaching practices displayed both commitments to ARSJ STEM teaching and improvement on practice. Participants who displayed weaker commitments to improve on practice tended to resist TTS support structures and required additional scaffolding. Across the data, I also found that all participants exhibited desires to draw connections between ARSJ teaching practices and STEM concepts and skills. However, tensions arose when it came to practical enactment. Together, findings suggest the need for more intentional development of both ARSJ STEM teaching practices and support structures beginning at the pre-service phase. I conclude the study by offering implications for TTS programmatic improvement and the wider teacher education community. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]