The aim of this study is to analyse the effect of a previously validated training program to pro-mote Mathematics Teacher Education for Sustainability (MTEfS). The training program, designed from a STEAM approach and called Pro-STEAM, involved 23 in-service Chilean teachers. For data collection, a questionnaire was administered before and after the Pro-STEAM program; and the design and implemen-tation of a statistical task relating to sustainability, within the practical phase of the program, was ana-lysed. The results show that: 1) following the Pro-STEAM training program, over 60% of the participants reached an advanced level in Sustainable Development Goals involved; 2) by designing and implementing the statistical task, they developed competences linked to the teacher learning objectives to promote Edu-cation for Sustainable Development. It is concluded that MTEfS is an emerging research agenda for creat-ing positive social solutions.