Improvement in technology, changes in cultural norms, and the expansion of opportunities has diversified American workforce. Small teams have become an integral part of how organizations accomplish tasks and achieve their goals. Many work teams are dynamic in their compositions with new members often being added to preexisting teams. However, our understanding of how teams function generally assumes a static setting with limited changes in group compositions and fails to capture the fluidity in group dynamics in the real-world workplaces. Our research bridges this gap by investigating whether and how a team, including old and new members, responds following an addition of a newcomer. Understanding how newcomers’ social identity affects their coordination and cooperation, and those decisions by the old team is relevant to organizations at all levels. Our work will shed light on how organizations could integrate newcomers from different backgrounds more successfully, thus improving teams’ performance and boosting productivity. This research also expands the frontier of our knowledge on how to forge a diverse workforce that will operate more efficiently on an aggregate level. It thus has direct implications for the output of the U.S. economy and that of the world economy.