Siempre Adelante, a support organization for Central American and Mexican immigrants and refugees in Los Angeles, provided adult Spanish literacy classes inspired by Freire's practice of critical pedagogy. A 13-month ethnographic study of intermediate Spanish literacy classes examined how "critical student agency" was fostered or hindered through classroom discourse. A literature review discusses the notion of "agency" through the work of major theorists, including Gramsci; Foucault and poststructuralist thinkers; and Freire, McLaren, and other theorists concerned with critical pedagogy. The study focused on classroom discourse as six students received Spanish literacy instruction from each of three teachers. The discursive practices during instruction differed so much between teachers that each teacher's class is presented as a distinct "case." In the first case, a teacher-centered "banking" system of pedagogy led to teacher and students co-constructing a "hegemonic discourse community" that limited the development of critical student agency. In the second case, the teacher's positioning of students as active social subjects helped teacher and students to co-construct a "counter-hegemonic discourse community" that fostered critical student academic and sociopolitical agency. In the third case, the students (with a notable lack of teacher participation) constructed a learning community that alternated between hegemonic and counter-hegemonic discourse but nevertheless fostered critical thinking. Numerous examples of discourse and classroom practices are given in appendices and throughout the text. (Contains references in each chapter and an index.) (SV)