Faced with the computerization of schools (since the existence of computers and internet in the units) and in view of the need for greater efficiency, effectiveness and productivity of educational units, the state of Minas Gerais implemented in 2008 the Minas Gerais System of School Administration (SIMADE) in all public schools of the state educational system. This administrative system allows the organization of educational data and, based on them, the proposition of actions, strategies and interventions in order to improve the quality of education. In this work, we investigate the use of SIMADE data as a management tool for the principals of the Minas Gerais state educational system. We use as an analytical reference the concepts of school management, data and self-efficacy of the director. A survey was applied to the directors and members of the staff of the secretariat of all schools in the state system. We obtained responses from 586 schools - in which the principal and secretary or technical assistant of basic education (ATB) answered the questionnaire - most of which attend Elementary and Secondary School. The main results are: (i) the principals have less time in the function compared to the secretaries and ATBs; although more educated, principals dedicate almost equal time to the administrative and pedagogical management; (ii) computers are generally in good condition, access to SIMADE is considered good and the frequency of access to the system is greater by the secretaries and ATBs, who were satisfied with the usability of the system; (iii) the principals are distributed in three levels of self-efficacy - low, adaptive and high; (iv) SIMADE is considered one of the most used information sources within the school. The use of the system, from the perspective of the subjects of the research, has more administrative than pedagogical purposes, although the details recorded in their answers about the use of the system show signs of more pedagogical use, indicating possibly different perceptions about the meaning of possible pedagogical uses of the system.