Science Olympiads and science fairs are effective instruments to foster interested and talented students. However, at most schools competitions are not systematically integrated into the school mission statement so that students are unaware of these opportunities. The purpose of this study was to investigate the effectiveness of a newly designed competition day in terms of willingness to participate in a science competition and to learn more about students’ reasons for a prospective participation. A project day (called ‘competition day’) for students in sixth grade was designed to encourage and motivate more students to participate in science competitions. The theoretical foundations for the design are self-determination theory and an adapted version of Holland’s RIASEC-model. The sample consisted of 474 German sixth grade students from six secondary schools. A pre-post-follow up-study was conducted with two intervention groups; both groups participated in the competition day and either entered a fictive competition or worked on the same tasks in school lessons. One control group not participating in the competition day was also investigated. The results provide information regarding students’ interests, as well as reasons for and against participating in competitions. Furthermore, the effectiveness of the competition day is shown. The competition day is an effective way to introduce students to competitions and raise their willingness to participate in science contests. Combining the competition day with science competitions showed even better results. This supports the call for continuous fostering strategies.