Proporcionalidad directa: una propuesta de desarrollo profesional docente

We present a professional development proposal for in-service mathematics teachers, which also includes a teaching sequence for secondary-level students centred on the topic of direct proportionality. The sequence developed serves as an example that illustrates a design model structured around three key dimensions: the consideration of the knowledge required by teachers for the teaching of mathematics; the incorporation of methodological principles specific to mathematics education; and attention to the difficulties reported in the literature regarding students’ learning of the mathematical content addressed—in this case, direct proportionality. We contend that this proposal, grounded in activities designed for secondary education and intended to prompt teacher reflection, contributes to the re-signification of teachers’ advanced knowledge, fostering a dialogue with the knowledge necessary for teaching at the secondary level.