This research sought to identify if the increase in average proficiency of pupils in basic education in the State of Tocantins occurred between the years 2001 to 2007 could be explained by improved qualification of Mathematics and Portuguese teachers who participated in training activities promoted by the Cesgranrio Foundation in the years of study. The relationship between teacher quality and cognitive performance of students are not easy to establish or measure, but in the current scenario of the research in the area of teacher effectiveness there is some evidence that the teacher is the most important factor explaining the performance of school students. The program of training conducted over six years emphasized the acquisition of knowledge and skills focused on participatory instruction and work in cooperative groups with students, accompanied by periodic applications of formative assessments to monitor progress of students. The proposed change in teaching practice in the classroom was supported by the systematic distribution of instructional material consisting of books for teacher and booklets of exercises for students. To evaluate the positive effect of the training program on students performance a research was conducted with 538 teachers who were enrolled in the first stage a lato sensu graduate program in School Evaluation in the areas of Mathematic and Portuguese. Variables defining participation and use of instructional material were derived from two questionnaires answered by the teachers These variables were shown to be correlated to the mean performance of students at their schools in 2007 controlled by the mean performance in 2001 and the results confirmed the hypothesis posed at the beginning that teacher training program can increase students learning at the eighth grade. Teachers that have a high degree of participation in the training program in Mathematics and frequent use of the instructional material distributed in Portuguese were positively correlated to improved performance. The conclusions of this work discuss the difficulties of conducting training programs, as a model for intervention in the academic performance of students in a concrete educational system. A program to improve teacher’s quality and simultaneous monitoring of student’s performance for a long period of time is not easy to implement. However, the study has drawn, from a particular experience at the State of Tocantins, suggestions and recommendations and extrapolated to the broader public policy of continuing education aimed to increase teacher quality and improve cognitive performance of students.