Children's physiological and emotional reactions to witnessing bullying predict bystander intervention.

Study goals were to explore whether children clustered into groups based on reactions to witnessing bullying and to examine whether these reactions predicted bullying intervention. Seventy-nine children (M = 10.80 years) watched bullying videos in the laboratory while their heart rate (HR) was measured, and they self-reported on negative emotion after each video. Bullying intervention was assessed by school peers. Two groups emerged based on reactions to the bullying videos: The Emotional group (43% of children) displayed HR acceleration and reported high negative emotion, whereas the Unemotional group (57% of children) showed HR deceleration and reported low negative emotion. Group membership predicted bullying intervention, with peers reporting that Emotional children were more likely to stop a bully than Unemotional children.