The effect of a training programme on teachers' conceptions about the nature of science and technology The themes of nature of science and technology (NoS&T) are considered key and innovative for scientific literacy and therefore the training of science teachers on these issues is needed. The effectiveness of a training model for secondary teachers in initial training along the lines of conceptual change suggested in research is tested. Teachers perform some explicit, reflective learning activities, based on the pedagogical content knowledge on a specific NoS&T topic (scientific research) and develop some self-evaluative reflections. The effectiveness of training is evaluated through a methodology that applies a longitudinal quasi-experimental pre / post-test design and uses an assessment tool based on ten items on scenarios. The findings show the teachers' individual profiles of conceptual change that allow identifying the specific areas where teachers change their previous ideas and the direction and intensity of the changes in their understanding of the subject; further, the changes for each of the ten assessment questions are identified, which reveal the complexity of conceptual change. Finally, feasibility, generalization and improvements proposed for the initial training model for science teachers is discussed.