Although there has been significant research investigating the processes that facilitate how individuals work collectively as a team, there has been little attention to the specific behaviors that individual team members need to exhibit to support teamwork. Despite two such measures currently existing in the literature, both suffer from a few important limitations, which makes it difficult to ensure individual team members are contributing to the team and targeted for the most appropriate developmental efforts. Through a series of studies, we inductively develop the dimensions for such a measure, establish its convergent and discriminant validity against an established peer-evaluated measure, and then show how it fits in the nomological network of established teamwork measures. The resulting measure supports the strengths of a multi-source, peer-rated scale by capturing observable behaviors that can more clearly be evaluated by fellow group members and which are applicable to various organizational environments.