This article analyzes the effects on the teaching practices carried out by three teachers from a primary school in Mexico City after they attended a training course.These three teachers developed a class of direct proportionality with the group they teach daily.The class were held after the teachers attended a yearlong course called Proportionality and its teaching.The course had a total of 25 hours of work distributed in monthly sessions and was carried out with an approach similar to that proposed in current official programs: teaching mathematics through problem solving.The analysis was made considering the stages proposed in this approach: instruction, a-didactic time, pooling of strategies and results and synthesis (or institutionalization) of the knowledge developed during the class.The data highlights the complexity of this form of teaching and its heterogeneous appropriation.