Developing students' systems thinking is an often-posed demand in education for sustainable development (ESD) and science literacy. Several studies have shown that systems thinking can be fostered in students of different education levels. Therefore, science teachers who are required to teach ESD-relevant topics should be proficient in systems thinking and be able to transfer that knowledge effectively to their students. The research project SysThema (Systems Thinking in Ecological and Multidimensional Areas) investigated the effect of three courses designed to foster systems thinking in student teachers of biology and geography. Courses varied in their proportions of technical fundamentals of system science and didactical content for teaching systems thinking. To conceptualise systems thinking, a heuristic structural competence model for systems thinking was developed. This model served as the basis for a test in evaluating the courses in a quasi-experimental intervention study that employed a pre-, post- and follow-up test control group design. After the completion of the courses, a high effect of fostering systems thinking was found in all treatment groups compared to the control group.