This research is a cutting from a broader research, entitled Institutional Contexts and the Construction of Teaching Quality in Basic Education and that has been developed since 2009 by SOCED - Group Research in Sociology of Education. We used empirical data derived from a survey composed of separate questionnaires to parents, students and teachers from ten schools, four public and six local private sector in the city of Rio de Janeiro. From questionnaire answered by teachers was obtained most of the data. The study investigated the role of the teacher in this universe from the analysis of data such as socioeconomic status, working conditions, career paths, pedagogical practices, visions and expectations about the students. We established a comparison between the best performing schools within the set investigated, one public and one private system, seeking to identify the characteristics of teachers and their practices that produce good performances students, regardless of the differences between the subsystems that are embedded in school. Based on empirical material produced, we raise some hypotheses about the teacher-effect in the production of well succeed school trajectories.