This article describes a scientific and practical journey through the worlds of mathematics education and development education/global education. It explores one link in detail: critical mathematics education and the competency 'mathematical modelling' in theory and practice. It describes a case study of a secondary school in Baden-Württemberg, Germany, based on a model of critical research. A central theme is the value of a holistic, self-organized learning process in which global and mathematical competencies and skills are combined. The research identifies the value such a process provides in helping students understand their role in a global society, including recommendations for schools, policy, and research.