Group projects are an important component of higher education, and the use of peer assessment of students' individual contributions to group projects has increased. The researchers employed an expectancy theory approach and an experimental design in a field setting to investigate conditions that influence students' motivation to rate their peers' contributions to team projects. Two questionnaires were also developed and tested by the researchers. This research found that rating format and rating frequency significantly interacted to influence student motivation and their perceptions of their team. Research findings reveal peer assessment to be a complex process in need of further study. Two peer assessment instruments and peer assessment training materials are provided along with suggestions for future research. (Contains 6 tables and 3 figures.)