Growing emphasis on elementary STEM education has pushed elementary teachers to face curriculum changes that focus on standards with which they are largely unfamiliar (Smith, 2020; Trygstad et al., 2013). As a result, elementary students are not always exposed to STEM subjects or integration and miss out on opportunities to access and enjoy the hands-on, inquiry-driven activities that accompany them. This deficit disproportionally impacts high-need, urban districts that serve Black and Brown children and families, thus perpetuating inequities in STEM education and careers (Tate et al., 2012). To address these issues, we designed a Fellowship program that strengthened K-12 STEM teacher leadership in local, high-need, schools. In this paper, we take a closer look at how five elementary teachers took on STEM teacher leader identities and then sustained and strengthened those even as program supports reduced. We asked: How do elementary teachers develop and sustain STEM and leadership identities through participation in a Master Teacher Fellowship? Using positional identity and selfefficacy lenses, we interpreted focus group interviews, coursework, reflections, and Fellowship meeting notes. Findings suggest that elementary teachers developed their identities gradually--first, as they recognized themselves as STEM "teachers"; next, as they recognized themselves as STEM "leaders"; and then, as others recognized them as STEM teacher leaders and positioned them to enact change in their schools and to support their colleagues. Implications for teacher educators shed light on how elementary teachers can be best supported in increasing STEM learning for their students across grade levels to effect school change.