This study focuses on collaboration between student musicians in a wind quartet, saxophone quartet and string quartet. Devised as an explorative investigation using observation and interview methods, the roles of student musicians are defined within and across quartet rehearsals over a period of four weeks. The data indicate that there are common roles assumed by student musicians in a quartet: leader, deputy-leader, contributor, inquirer, fidget, joker, distractor and "quiet one". The students represented one or more of these roles during a rehearsal and sometimes changed roles across rehearsals, normally through compensating for each other's mood changes. Quartets with a regular leader exhibited more stable team-role behaviour, a consistently focused group dynamic and better progress than those without one did, highlighting the impact of leadership on non-leadership roles and the success of a group. (Contains 2 notes and 8 tables.)