EDULOG (an initiative by the Belmiro de Azevedo Foundation, which aims to contribute to the construction of a reference education system) and researchers from the Nova SBE Economics of Education Knowledge Center and from the University College London developed for the first time a study that allows evaluating the influence that a professor has on the evolution of students learning in public schools, through the Teacher Added Value (VAP). The study shows that if all teachers had the impact of their best peers on the students, their grades could improve significantly. This positive effect is most evident in Mathematics, rather than Portuguese, the other discipline analized.