In recent years, research on the professional development of young-learner language teachers has grown in an attempt to draw its boundaries in comparison to adult-learner teaching. However, little comparative research is available on the professionalism of young- and adult-learner teachers, especially on their social justice-oriented practices. Motivated by this conspicuous gap, the present study explored Iranian young- and adult-learner teachers’ social justice practices and the contributions of such practices for their professional identity construction. Data were collected from an open-ended questionnaire, narrative frames, and semi-structured interviews. Data analyses revealed that while the teacher groups were similar in relation to promoting social justice at the class (equal participation and group work) and institutional (developing communal sense of justice-oriented practices) levels, the young-learner teachers differed in focusing more on self-inquiry approaches to promoting just instruction. Such practices also defined the participants in claiming and adopting the identities of caring, supportive, powerful, and critical teachers. We conclude with implications for teacher educators regarding how to anchor the principles of social justice into teacher education programs in order to positively shape teachers’ developing identities relative to their proficiency level of teaching.