Purpose: Deficient group processes such as conformity pressure can lead to inadequate group decisions with negative social, economic, or environmental consequences. The study aims to investigate how a group technique (called INFO) improves students' handling of conformity pressure and their collective judgments in the context of a transdisciplinary case study (TCS) for sustainability learning. Design/methodology/approach: The improvement of normative functioning and output (INFO) group technique was tested in a field experiment embedded in a TCS. The INFO technique involves individual and group assessments of task difficulty. The experiment compares the performance of student groups assigned to control and experimental conditions in estimation tasks related to environmental planning and rail traffic. Findings: The INFO interventions significantly improved the accuracy of group estimates compared to the control conditions. Applying the group technique could promote student's learning and facilitate the search for sustainable solutions in a TCS. Practical implications: Results indicate that individually and collectively analyzing and discussing difficulties of a task as suggested by the INFO group technique can help students improve collective judgments on real world issues. Originality/value: Group techniques are a prominent type of TCS methods as group processes are crucial for sustainability learning. First, this study applies the INFO group technique in a TCS in order to evaluate and further develop the technique. (Contains 2 tables and 1 figure.)