This paper aims to present the results of an investigation regarding the professional development of teachers who worked in the early years of basic education. The qualitative research involved teachers who participated in the "Observatório da Educação" project (MEC/CAPES). Because of the data amount, we choose to present the data analysis based on the work of only one teacher, who is considered as a legitimate representative of the whole group. All data were collected through direct observations, recordings, questionnaires, interviews and reflective "relatorios" on the implementation of the activities to their students. Data analysis was based on Ponte, Garcia, Shulman and Serrazina' studies, researchers that study the development and professional knowledge or reflection. This study reveals that the experiences during the training process favoured the redefinition process of mathematical content and teaching beyond reflection on practice.