Science fairs have been for many years a popular school activity in North America. They are a venue for the popularization of science and consequently an important encouragement for the pursuit of careers in science or engineering. However, little is known about students' perceived motives for participating in local or national science fairs and about the way in which their involvement mediates their interest in science learning and scientific careers. The present study investigates the motivational factors associated with the high school students' decision to participate in the 2008 Canada-Wide Science Fair, a thoroughly selected and highly motivated group. Our study examines 5 sources of motivation: (1) interest in science content, (2) sense of self-efficacy, (3) assurance of achievement through rewards or gratifications, (4) the social aspect of participating and (5) working strategies to gain scientific knowledge and methods. The understanding of the anticipated benefits participants seek through their involvement in science fairs may have the potential to help science teachers adapt instruction to appeal to a broader range of students in schools, thus nourishing the emergence of more interest in science.