This study concerns a professional development course designed and implemented for prospective teachers, centred on a teaching method regarding problem-solving activity, namely, the Thinking Classroom. The study is framed in the theory of cultural transposition, a perspective about the encounter with teaching practices from different cultural/school contexts. Cultural aspects are considered crucial and this encounter between cultures is seen as an opportunity for actors to become aware of their own unthoughts, i.e., some of the 'invisible' cultural beliefs about teaching and learning absorbed by their own culture. According to this framework, we present the results from a questionnaire given to all the participants, and two case studies of prospective teachers involved in the professional development, in order to discuss the kind of unthoughts on which they have focused in thinking about this training experience.