Education reforms in the United States and abroad have increased efforts to improve student interest and capacity in STEM (science, technology, engineering, and mathematics). Despite these attempts, students still have little opportunity to engage in STEM learning in K-12 education. This qualitative case study was designed to investigate how incorporating STEM into teacher education can promote STEM teaching as well as enhance math instruction. The study took place in the fourth year of an undergraduate teacher education program spanning a secondary math and science Methods course and student teaching. Guided by the framework of sense-making, individual interviews, teaching artifacts, and written reflections for four teachers were analyzed to identify moments of dissonance that pushed participants to reach new understandings about the learning and teaching of math. Findings indicated that learning to teach math through the lens of STEM shifted pre-service teachers' instructional emphasis in two ways: 1) figuring out math vs. learning about math; and 2) teaching math through authentic STEM contexts as opposed to focusing purely on mathematics. However, experiences in student teaching can either enhance or stifle these gains. Findings suggest the role of teacher education in promoting STEM education by shifting prospective teachers' mindsets about mathematics and teaching.