**5. Discussion and conclusion**

Since 2010, the ITT model of the University of Lisbon has intended to create conditions for the student-teachers investigate their own practice. By doing this, this model makes the student-teachers not just consumers of educational knowledge, but also producers of knowledge derived from their own practice.

The acquisition of professional knowledge is influenced by the experiences and conceptions of teaching [21]. Teachers hold different conceptions of teaching, namely traditional experimentalist, constructivist and social [35]. Thus, it is essential to identify student-teachers' conceptions of teaching, to bring it to awareness and to discuss how these conceptions influence their curricular decisions. Within this ITT model, while involved in the design of the didactic proposals, student-teachers were encouraged to interpret the formal curriculum and turn it into a teaching curriculum. And so, they were led to critically reflect on the curriculum, considering such elements as what, how and why to teach this particular subject, and to consider the relevance of the subject taught for students and for society. In addition, student-teachers researched the implementation of the didactic proposal within the classroom. This moment required them to identify a previous research problem, to collect and analyze data and to reflect on students' learning and difficulties, as well as on conceptions affecting their decisions and actions. So by developing and implementing a didactic proposal and by researching their own practice, student-teachers were not only developing theoretical knowledge, but also they were using it to make sense of their teaching experience. In this process, they were confronted with tacit conceptions, which were analyzed and changed.

These experiences facilitated the development of professional knowledge. Indeed, studentteachers developed didactic proposals sourced on educational literature and deeply explored and discuss it in collaboration with the university teacher and the school teacher. The relationship between the university teachers and the school teacher, as recommended by educational research [36], encourages the connection between theory and practice, as student-teacher bring to the classroom "fresh" theoretical knowledge which will be put into action and tested in straight collaboration with the school teacher and his/her insights from the practice. In addition, the reflection about their practices and its impacts on students' experiences, supported with educational knowledge, assists them in building new meanings regarding practices and facilitates critical analysis of previous conceptions at the light of evidences that they collected during their practices.

Student-teachers evaluated positively this ITT model as they had the chance to experience different situations: (1) Discussions held with the educational researcher and school teacher, (2) Designing investigative learning tasks, which improved their didactic knowledge, reasoning and communication competencies, and (3) Researching their own practice, in order to reflect on the impact of their practice on their students' learning and to understand the influence of tactical conceptions on their practice.

However, despite the importance attributed to the reflection and to the construction of professional knowledge by the teachers as a way to break with non-reflected practices and conceptions, research show that teachers' practices remain more or less unchanged [37]. Even beginning teachers involved in recent innovative practices in contexts of ITT tend to adopt more traditional ones when they are placed in contexts of professional practice [38]. So despite the positive evaluation made by the student-teachers about the ITT model presented in this paper, it is important to have in mind that this was a sole experience and to wonder about the durability of its impacts on student-teachers. Indeed, one thing is being involved in a context of teacher training, and another thing is the deliberate will to keep on changing and implementing innovative practices that require effort, confidence and also a supportive school. Considering this, two questions emerge from this study. How do student-teachers transpose knowledge constructed during an ITT experience to contexts of professional practice? How to make the impact of ITT experiences last when student-teachers are involved in contexts of professional practice?
