Abstract: This paper presents the results of an ethnographic study of two in-service physics teachers' participation in a seminar of the master's degree program on teaching science they are studying at the National Pedagogical University (UPN in Spanish) in Bogotá, Colombia. In it the two teachers work with an advisor to plan, implement and report the results of an educational proposal aimed at secondary school students. The ethnographic analysis yields elements for reflecting on continuing teacher education: the multiple meanings contained in the teachers' practices and shared assumptions; the work undertaken jointly between the teachers to explain, confront and negotiate these meanings; and the teachers' commitment to their students' development.