In European universities, teaching ethics has acquired special relevance with the Bologna Process and changes in curriculum. In Spain, the White Book of the Degree in Information and Documentation incorporates ethics as a specific competence, through the combination of ethical, social, and legal content, as a transversal competence. In this context, this study aimed to detect whether changes in attitude toward ethical values occur in a group of LIS students as a consequence of the training received and to test a qualitative approach to identify these changes. A questionnaire based on the vignette technique was used, presenting students with cases of conflict or ethical dilemmas, in most cases in the context of an information unit. For each vignette, they were asked to assess the performance of the information professional and to explain what they would have done if they were in their place, before and after they received the training. The results obtained showed that the attitude of the students who received training changed from individual ethics to professional ethics. We can consider that the content used for the training was correct, although the knowledge about the different ethical theories and ethical reasoning models for decision making should have been deepened. To the theoretical content, we must add a teaching methodology based on the effective study of cases and scenarios in our work. On the other hand, the application of the vignette technique and content analysis as a methodological approach to the students' discourse is very useful, since it was decisive in identifying the reasons that helped the students make a certain decision, before and after the training session, for checking to see whether this decision was made following their individual ethics or guided by normative ethics, and for knowing the degree of acceptance and depth of the training session.