As education is a powerful means of promoting sustainability, it is necessary to think and act on the (trans)formation of the professional profile of the future kindergarten teacher. As ecocentric educational practices can be a crucial point, ecocentric action competence needs to be developed. In this context, pedagogical traineeship supervisors can play a meaningful role. Accordingly, this study analyzed the didactic-pedagogical potential of a training strategy in science teaching based on reflection-critical thinking about what effective science teaching is. Further, it investigated the mediating role of action research methodology in promoting trainee reflexivity. The findings highlighted the merits of the formative perspective adopted, given the learning evidenced by children and stated in the traineeship report. It is concluded that the role of the supervisor is relevant in the construction of a pedagogical outlook of science teaching aligned with environmental values. It is time to take the traineeship process as a space to understand and identify pathways for empowering ecocentric action.