This article shows the results from a research, whose main objective was to help basic education teachers to think about the mathematical activity they promote in their students during class. Consequently, we suggest a model of reflection that could help the teachers to analyze specific aspects in their teaching practice. This document describes the elements in which this model was made, and it also shows some of the results from the reflective process of two teachers (one from pre-school and the other from junior high school). Their considerations on the subject allowed them to focus their attention on their students’ mathematical activity, to anticipate the probable answers, and to be aware of the learning disabilities. In regard to the planning before carrying out the model, we evaluated the design of the activities with a clear mathematics learning purpose.