The relationship between past teamwork and task-related experiences, attitude toward teamwork, collective efficacy, and task performance among undergraduates (N = 298) assigned to group projects (N = 48) in 2 different Food Science courses was examined. The results of survey data collected at the beginning and end of the projects showed that past teamwork and task-related experience predicted individual student efficacy at the end of the project, and that starting efficacy, but not attitudes toward teamwork, mediated that relationship. Convergence over time among team members' efficacy, and diversity of past task-related experiences was positively related to project grade, whereas diversity in past teamwork experiences was negatively related to project grade. The relationship between past experiences, attitude toward teamwork, efficacy, and grades did not differ between the 2 courses. Implications for practices of implementing group class projects are discussed.