This paper is part of a master’s essay on Brazilian Education and has as its focus the analysis of intra-school factors and their influence on students’ development. The study was carried out in a public school in Rio de Janeiro which presented improvement on school results, based on IDEB’s data (Elementary to High School levels development rate ), between 2005 and 2007. Aiming to integrate, quantitative data brought by external evaluation statistics of school’s daily routine, an ethnographic approach was applied as its methodology. The researcher remained completed involved in work field for six months, collecting data through observation, interviewing directors, coordinators, teachers and staff, performing activities with students in the classroom and analyzing school papers. Studies of sociology of schools by Rui Canário and João Barroso and also researches on effective schools in Brazil, the United States and England were all used as a theoretical background. Analyses show the predominance of institution effect on school results characterized by the interdependence of intraschool factors. However, there is a strong influence of the management and organizational aspect on school atmosphere’s definition and, consequently, on students performance. It is suggested that educational policy invest in resources’ decentralization, in constructing schools’ pedagogical and administrative autonomy, in training focused on teacher’s practice, in professionalizing management and in school’s good ecological conditions.