Carried out with six elementary school teachers, this action research aimed to co-construct and implement differentiated pedagogical practices in writing to students from disadvantaged backgrounds. This text presents the results of the training component (Guay & Prud’homme, 2018) of this action research and documents the effects of the participation of teachers in this study on their professional development. The results show achievements in all dimensions of the Clarke and Hollingsworth (2002) model. The analysis of the cost/benefit ratio and the sustainability of the achievements puts into perspective the conclusion on the effectiveness of this type of professional development device.