Groupwork has become ubiquitous in language education, with the clear benefits of interaction and output on language acquisition. A body of research has investigated this interaction in pairs and small groups, and there is an increased understanding that individual group context is a key factor in determining the behavior of students. This article reports on a study that first investigated emergent leadership within groups, and the influence of the group on leader stability. The study then examined how leadership is represented in student task engagement. Students were placed into fixed small groups for the first semester, and then allowed to self-select into groups for the second semester. Perceptions of leadership were measured three times in each semester, and leaders were identified in each group. Results showed that changing group membership had a considerable impact on leadership stability, and student interaction was then analysed to determine how leadership influenced engagement with tasks. Students with high leadership displayed high engagement with tasks, and took a central role in driving the conversation. When a student chose to reject the role of leader there was a dramatic impact on their engagement in conversation. The stability of leadership and its impact on performance has practical implications both for researchers and teachers.