Disturbed by inequities created by tracking, many schools have attempted to "detrack" by consciously organizing students into academically heterogeneous classrooms. This paper, based on a year-long interpretive study of a detracked ninth grade English-History "core" program at a diverse urban high school, focuses on the encounter between the core teachers' progressive teaching practices in their detracked classrooms and the "unofficial" (Dyson, 1993) social worlds of the students who were enacting those practices. Highlighting small group work as a critical point of convergence and tension between these two classroom worlds, this paper describes how the racially and socioeconomically polarized nature of the overall school context framed and permeated students' interactions in the detracked class, leading, at times, to a reiteration of the very inequalities which detracking was designed to address. It considers the challenges of teaching for social justice in racially and socioeconomically divided settings, and offers suggestions for practice. (Contains 33 references, 8 notes, and 3 tables of data.) (Author/RS)