Those responsible for supervising teacher candidates have an obligation to promote socially just pedagogies. In this paper, I investigate my own supervisory practice as a novice supervisor in my mediation of a teacher candidate's understanding of social justice. I rely on a sociocultural theoretical perspective (Vygotsky, 1978) and the psychological tool of responsive mediation (Johnson & Golombek, 2016) for my supervisory practice and an anti-capitalist interpretation of socially just teaching (Apple, 2004; Ayers, 2010; Bowles & Gintis, 2011). Through a microgenetic analysis (Wertsch, 1985) of a post-observation transcript, I empirically document the developmental opportunities that take place over a span of 15 minutes and how my responsive mediation shaped how the teacher candidate shifted to talking about socially just teaching differently. Implications for an expanding conception of social justice in supervision and the introduction of a theoretical perspective for the dialectical unity of supervision and teacher candidate development are discussed.