Science fairs can be good motivators, but as extracurricular activities, they leave some students behind. However, by staging a Science Challenge Day at school, educators can involve all students in doing everything from choosing activities to judging projects. This article presents a model for running a successful Science Challenge Day. The author and her colleagues conducted a Science Challenge Day during a recent year to meet the International Baccalaureate Organization's requirement to assess personal skills: self motivation, perseverance, teamwork, and self-reflection (IBO 2007). The event can be used for much more, however. It could help assess any number of laboratory process skills, or, with a specific theme, it could reinforce classroom concepts. They found the event to be genuinely fun while also letting students work in teams, apply their critical-thinking skills, and compete in a non-traditional manner.