This 10-week study investigates the relationships between diversity beliefs, teamwork satisfaction, perceived classroom competitiveness, and attitudes toward project-based activities among 105 marketing students. Findings indicate that diversity beliefs enhance teamwork satisfaction, whereas performance-approach goals reduce it. Classroom competitiveness negatively moderates the impact of teamwork satisfaction on project attitudes, whereas teammate competitiveness has a positive moderating effect. These insights can help educators balance competition and collaboration to optimize learning environments.