Introduction: Despite State efforts to set up an education based on constructivism, has not modified the teacher's traditional conception of teaching neither their students' perception as passive subjects of learning. However, the conceptual change in teachers is not an automatic process, because it requires an epistemological shift, and understand how it is put into practice the pedagogical dimension of constructivism. Method: We invite to 3 private, 3 public, and 3 subsidized schools of Santiago de Chile (Chile) to participate in dyads of teachers with primary and secondary education. We applied a questionnaire on teaching and learning dilemmas (Pre-test). The first phase consisted of a course-in-the-university to plan a collaborative constructivist teaching. In the second phase were selected some teachers' dyads to observe their classes and their reflective process, supporting them with a device intended to produce reflection. Half of these dyads had the additional support of an expert. Each dyad participated in 5 sessions of reflective practice. The device combines video with questions about the teaching observed, and the application of their own classes discussed. Dilemma Questionnaire was applied as post-test. Quantitative and qualitative information analysis was developed. Results: The obtained data tends to show a significant change in the group with additional direct mediation respect of which only got the device to reflect. Qualitative analysis yields adequate levels of professional reflection, and a move to mixed teaching practices. In addition, the data suggest conceptual change regarding the necessary relationship between skills and content in student learning, and the need to restructure prior knowledge. Some knots of resistance were time and diversity of students. Discussion and Conclusion: It is possible to stimulate conceptual change regarding constructivist teaching in-service teachers, especially when specific devices are used to produce reflection on the teachers organized in collaborative dyads. These devices produce progress on the level of reflection, beliefs about teaching and learning and teaching practices, but schools must provide conditions to ensure that this work is done on a regular and systematic way. © Education & Psychology I+D+i and Editorial EOS (Spain).