Solid teacher training can be a transcendental tool in solving the most pressing environmental problems of our time. The purpose of this study was to reinforce the competencies of in-service teachers through a training process on environmental and sustainability issues. The research was carried out during the 2020–2021 cycle in Preparatory School No. 47 of the Autonomous University of Guerrero. We sought to broaden the teachers’ knowledge of environmental education for sustainability, the sustainable development goals and methodological strategies. The information was collected through an initial questionnaire, as well as the record of teachers’ activities during the course, which was structured in four topics: socio-environmental problems, environmental education for sustainability, sustainable development goals 2030, and methodological strategies. The training process influenced the teachers’ perception, achieving a more complex vision of the topics studied. The didactic and pedagogical strategies proposed facilitated the integration of transversal activities in their discipline. The work carried out demonstrated the importance of strengthening training processes that include methodological strategies such as transversality taking advantage of the physical characteristics of the rural community. Teachers develop environmental competencies for sustainability in their educational practice, to contribute to the integral formation of their students.