Evaluación del conocimiento pedagógico del contenido para enseñar matemáticas elementales

We present a study that allowed for the development of an instrument to assess a component of pedagogical content knowledge to teach mathematics: the teacher's knowledge about how students learn mathematics. This component has been described theoretically by other authors but could not be assessed reliably in mass testing. In the outcome of applying the instrument to different groups of people, we identify certain aspects of knowledge that cannot be explained by the disciplinary knowledge, although is affected by it. This kind of knowledge is detected particularly in primary school teachers with specialization in mathematics, both in service and in training.