Numerous preservice primary school teachers begin their training with a negative attitude towards mathematics: this phenomenon can have important consequences for their training path and for their future teaching. How teachers' training programs could affect preservice teachers' attitudes is one of the main issues in research on future teachers in the field of mathematics education. However, longitudinal studies developed during specific teacher development programs are still rare in the research field of teacher development. In this frame, this paper reports on the results of a longitudinal 2-year study carried out within the initial training of 35 preservice primary school teachers. According to the three-dimensional model of attitude towards mathematics, we developed the analysis of future teachers' emotional disposition towards mathematics, vision of mathematics, and perceived competence in mathematics, at the beginning of the training path and after 2 years. We found two main results on two different levels. First, a positive change in future teachers' attitude towards mathematics, generalized over all the three dimensions, occurred during the training period, and this result opens the issue of the relationship between formative choices and change in attitude. Second, our data confirm the strong relationship between the three dimensions of attitudes: every change in one dimension affects the other two dimensions.