This 2-year qualitative case study focuses on one emergent mathematics teacher leader, Mr. Miller, and his conceptualization of Social Justice Mathematics (SJM). SJM is a justice-oriented pedagogical approach where students simultaneously learn dominant mathematics and explore social injustices to take action toward justice. Using Rodriguez's (Journal of Research in Science Teaching, 1998, 35, 589–622) sociotransformative constructivism framework, findings illuminate how dialogic conversation, authentic activity, and metacognition supported Mr.