Though teamwork is a mainstay of corporate America and business academia, individual assessment and compensation are problematic in disciplining and removing teammates who are free-riders and rewarding high performing team members who bear a disproportionate burden of the project. Therefore, the authors set out to develop and test an assessment instrument for peer assessment of teammate performance that measures both the critical dimensions and outcomes of teamwork. The findings in this research can be used to guide teachers, students, employees, and employers in forming, monitoring, and appropriately evaluating team members' performance. It can also help a member of a team to be a more effective teammate.