The agency of primary school students has been studied increasingly in recent years; yet, we know relatively little about student agency in music educational settings or how students experience their participation in joint musical action. This study explores sixth-grade students' experiences of their agency in whole-class playing. Qualitative content analysis of 11 pair interviews identified vulnerability as an essential element of participating in whole-class playing, highlighting the intrinsically emotional nature of the process, the immediacy of the musically shared moment and the safe place of entrainment. This study elucidates the enactment of agency and the resources facilitating and limiting agency within the context of whole-class playing from the perspective of students themselves.