The study presents evidence and analyzes the variables related to the average number of students per teacher in Brazil. Based on data published in the 2020 School Census, ten case studies were carried out in state and municipal networks that represent extreme situations, in order to understand the factors that contribute to teachers working with larger or smaller total numbers of students. Currently, almost a third of Brazilian teachers in the final years of elementary school have more than 300 students. This number is very high compared to other countries. The large volume of teaching work negatively affects the health of teachers, causes losses with absenteeism and the need to replace professionals, interferes in the quality of teaching work and impacts on student learning. This report is a partnership with Fundação Carlos Chagas (FCC) and Itaú Social.