Education for sustainable development (ESD) is intended to enable individuals to shape a fair and sustainable society. Implemented at schools, ESD addresses specific topics, e.g. "globalization" or "pollutants in clothing". This study investigates what challenges are connected with such issues in class and how students deal with issues of sustainable development at German secondary schools. Several teaching units in different subjects and schools were video- and audiotaped. The empirical material was analysed using the Documentary Method (a qualitative reconstructive approach) to describe students' competences that emerged within different pedagogical arrangements. We identified three key competences that provide important skills for handling issues in ESD that deal (1) with the state of not knowing, (2) with perspectivity, and (3) with calls to action.