In this article, we focused on sustainable development in mathematics education from the point of view of academic literacy in mathematics (ALM). ALM was understood here through three integrated components: mathematical proficiency, mathematical practices, and mathematical discourse (languaging). ALM skills support 21st Century competences which are important for citizen skills. Both ALM skills and 21st Century competences support lifelong learning and sustainable education. Citizens of future society need both ALM and 21st Century competences to model and solve the issues of sustainable development. We want to develop prospective teachers’ content knowledge and pedagogical content knowledge of school mathematics in the spirit of sustainable education. As the case, we chose the mathematical symbol “2/3” and how collaborative mean-ing making for “2/3” influences prospective class teachers’ interpretations. Col-laborative meaning making is part of ALM. Collaborative working as a tool for meaning making supports the other parts of ALM. By languaging different meanings for “2/3” in pairs, prospective class teachers deepened their under-standing about fractions. By supporting ALM skills in teacher education, future class teachers can have a more sustainable basis to teach mathematics for children. As a conclusion, based on the results of our case study, we summarized objectives for sustainable development for teacher education, teachers, and stu-dents in mathematics education.