This article explores challenges for knowing and learning in evolving knowledge fields. Legal education is chosen as a particularly interesting case as the knowledge field of law is expanding to international law with a multitude of actors, obligations, conventions and interpreters. In the current study, students’ group work with case assignments was observed and interviews with students and teachers conducted within a course in public international law. The following question was examined: What learning challenges do the students face when solving cases in international law? By employing sociomaterial perspectives on navigation as finding ways to interpretational possibilities in evolving and complex constellations of procedures, texts, and various actors in the knowledge field, the study pursued an analytical interest in how professional resources were assembled in the students’ work, and how such assemblages served to order practice and justify their decisions. The analysis showed that the students’ previously learned strategies for linking authoritative texts and questions in defining and solving legal problems were challenged by less stabilised constellations of textual sources and interpreters of law. The analysis also revealed tensions in the course setting between demands of navigating more open knowledge landscapes and expectations about student behaviour in current educational practices.