The aim of the present research was to uncover the opinions of future teachers about whether the formative knowledge of education for sustainability received in seminars during their practicums improved their competencies in sustainability and their values in educational teaching for their future classroom practice. The study entailed qualitative research with a thematic analysis. Semi-structured interviews comprising 14 questions, which were validated by 15 experts, were used to solicit the opinions of 52 future teachers with respect to the importance of sustainability and the development of intercultural competencies among their students. The information from the interviews was analyzed using thematic analysis on the basis of education for sustainable development (ESD). We conclude that the teachers’ practicum placements and training experiences were very positive because a lecturing pedagogical approach, taught via practical application in a school environment by an expert of recognized prestige, can be a useful resource to develop awareness of both sustainable development and its education, as well as to learn didactic strategies to apply ESD, which addresses aspects that are relevant in multicultural contexts, such as tolerance and empathy.