Resumen

Background: an important field of research in mathematics education is the initial training of teachers where deficiencies in the disciplinary and didactic knowledge required for their profession can be evidenced. Objective: to study the transformation of the specialized knowledge of future teachers about division of fractions. Design: qualitative descriptive paradigm where a case study is approached. Context and participants: a group of three students who design, reformulate and implement mathematical tasks during their initial training in a lesson study environment using the didactic analysis method, where they receive feedback from their peers and trainer. Data collection and analysis: data collection is obtained from the written productions of future teachers and the record of recordings of class discussions, which were analyzed using the content analysis method and the categories of the specialized knowledge model. From the math teacher. Results: future teachers show a change in their knowledge, starting their process with the design of a problem situation with a different meaning in the conceptual field of division of fractions, which becomes a problem situation with a multiplicative structure of the type "isomorphism of measure". Conclusions: deepening the processes of transformation of the specialized knowledge of future teachers from their first formative stage can give us insights on how to improve their training aiming at their professional teaching development.