Investigated developmental and gender-related trends in 2nd, 5th, and 8th graders', undergraduates', and adults' reactions to simulated bicycle collisions. Recently, scientists have called for exploration of the developmental mechanisms that underlie childhood injury. Our laboratory has, in three separate studies, demonstrated age-related decreases in beliefs about the negative consequences of bicycle collision. These developmental decreases in the expected seriousness of outcome parallel age-related increases in injury risk. The present study examined two alternative explanations for cognitive differences that might be related to increased risk for bicycle injury with increasing age. Contrary to predictions, however, age and gender were unrelated to subjects' expectations for whether a collision would take place, be actively avoided, or fail to take place. Similarly, age and gender were unrelated to whether subjects believed they could remain safe, that safety equipment (e.g., helmets) would keep them safe, or that different behavior would keep them safe. Results fail to support these expectations and beliefs as alternative explanations to developmental and gender-related trends in bicycle injuries, and indirectly suggest the importance of children's beliefs about the seriousness of injury as a contributer to injury risk behavior.