The first interaction of students in tertiary education with the work-integrated learning environment happens often through cooperative education or internships, where students, as emerging professionals, develop technical abilities and practice critical ethical decision-making and professional values. Accordingly, this study aims at assessing the impact of cooperative education on students' understanding of business ethics issues, by focusing on the differences in students' perceptions depending on work-integrated learning experience, academic majors and ethics courses taken. Testing our hypothesis on a sample of 234 business students at a Saudi business school, the results showed an evolution process of ethical perceptions, which indicates a maturation of ethical behavior due to the business environment exposure and not only from practical training or any other single factor. It also showed the insignificance of ethics education in this process as students' ethical values develop over time during their lives toward society's expectations rather than being shaped through formal exposure.