The thesis studies the meaning of Scientific Literacy, at the threefold level of its cultural, political and sociolingustic dimensions. It focuses on what extension the Biology teaching in high schools enhances the development of Scientific Literacy, in relation to relevant social issues, such as the environment. The research is carried among low income high school graduates nowadays enrolled in CPVCs (community classes in poor neighborhoods preparing high schools graduates to overcome the selective process of university entrance examinations). The study of the Scientific Literacy levels is referred to the competencies matrix developed by ENEM (the National Examination on Senior High Schools), insofar as the proficiency levels demonstred by 2783 high schools graduates enrolled in 97 CPVCs. The research was complemented through semi-structured interviews with teachers of those CPVCs. The thesis conclusions stress on the need of carrying a critical revision of the Biology teaching among CPVCs, since their pedagogical project is mostly targeted at the propedeutic aim of succeeding in the university entrance examinations. The thesis proposes then the development of teaching procedures that stress criticism and social- political participation, in order to overcome exclusion practices in schooling, such as those carried out by social movements.