This study presents a specific analysis of the treatment of the topic “similarity” by several college textbooks, in this case six Indonesian textbooks. The choice of this mathematical topic is justified by the fact that it requires in the activity of the pupils an implementation of both the geometric register and a numerical register, that of ratios and proportions. Thus, it is appropriate for the development of a general validity reference model, which will require further studies. The two points of theoretical support in the present study were the epistemology of the mathematical topic under consideration and the notion of praxeology, pertaining to the anthropological theory of the didactic. In addition to the meticulous review of textbook contents, the sketched model allowed us to evaluate the proximity of similarity treatments in a textbook and in the formal assessments of students at the end of college.