This article examines the development of professional knowledge in pre-service mathematics teachers. From the discussion of a task associated with the multiplication of consecutive integer numbers, generalization is recognized as a process that allows to explore, to explain, and to validate mathematical results, and as an essential ability to develop in the teaching of arithmetic, algebra, and geometry by using various representations. The study was conducted during three sessions of a didactic mathematics course, in which the instructor and ten students participated. The conversations of each session were recorded on audio and video. It was found that the reflective conversation fosters this knowledge from questions about the nature and processes of construction of mathematical concepts from a mathematical and didactic point of view.