In this study, we implemented a visual illusions contest as an educational activity within the practical programme of the subject "Perception and Attention" (Bachelor's Degree in Psychology). The contest was evaluated by verifying its effectiveness as a teaching tool for achieving the competences assigned to the course. We designed questionnaires for evaluating its effectiveness that were given to the students at the beginning and end of the course. The statistical analyses show that there are significant differences between the students' knowledge of the psychological processes before and after the activity (A2 competence). There were also significant improvements in the use of bibliographic and search resources (C3 competence) between the initial and final questionnaire. We conclude that the proposed activity is effective as a teaching tool for helping students achieve the core knowledge of the subject and its assigned competences.