Systemic equity challenges in K-12 STEM education place students from minoritized groups on an uneven footing, restricting access and opportunity for the diverse students who make up the majority population in US public schools. Teachers play a key role in advocating for equity and justice in STEM education. In positioning themselves as agents of change, they have the power to impact their classrooms, schools, and communities. Using a collaborative coding process informed by dominant and critical framings of equity in STEM education, we analyzed equity research presentations and final written reflections from a graduate course for practicing teachers (n = 23) focused on STEM integration. Teacher participants demonstrated one of four advocacy orientations: (a) equity in classroom teaching, (b) STEM education, (c) equity in STEM education, or (d) neither equity nor STEM. Our analysis of teachers' final course reflections led us to develop a rubric using principles of grammar to evaluate the levels of agency evident in teachers' statements. Most teachers were at least minimally agentic for STEM, but fewer teachers were agentic for equity. Only four of 23 teachers were highly agentic for equity in STEM education. We identify a need for more purposeful scaffolding in professional learning to build teacher advocacy and agency for equity in STEM education. Future research should explore the high-leverage practices in STEM teacher education that foster advocacy and agency.