Our teaching conception acknowledges the teacher's central role as a decision maker, influenced by knowledge, beliefs, and emotions. We believe that teachers' education must be focused on teachers' awareness of the complexity of the teaching process, of the incidence of these factors in it, and of the importance of looking at theory as a strong component of their professional development. In this framework, we face the question of the relationship between theory and practice, taking into account some aspects of our Project on Early Algebra (ArAl), which is also an in-service education process. We present the main features of the Project, highlighting not only its influence on teachers' knowledge and beliefs--and, consequently, on their practice--but also the way in which an analysis of such practice has given us a greater awareness of teachers' difficulties in reshaping their teaching, as well as some indications for our future research. (Contains 15 footnotes.) [For complete proceedings, see ED500857.]