To prepare emergency response organisations for collaborative work in unpredictable and dynamic situations, various types of exercises are widely used. Still, our knowledge of collaboration exercises with emergency response students is limited. This study aimed to contribute to this field by exploring boundaries that emerged between collaborating organisations in exercise activities and how these boundaries could be understood for learning. Drawing on the Akkerman and Bakker framework of boundaries as learning mechanisms, this study explored an exercise, including full-scale scenarios and seminars with students from the police, ambulance and rescue services education in Sweden. Thematic analysis of interviews and observations illustrated boundaries that emerged regarding vocabulary, prioritisation, roles, knowledge gaps and overlapping responsibilities across organisations. Rather than dissolving boundaries, this article suggests that boundaries can be utilised in exercises to support the students to contextualise their knowledge in relation to the demands of collaborative work. The concepts boundary work and boundary awareness were suggested to capture more generally the dynamics of learning in exercise contexts.