This research examined the development of stress responses across second to sixth grades and whether exposure to peer victimization alters stress response trajectories. Youth (338 girls; 298 boys; Mage = 7.97 years, SD = .37) reported on stress responses; teachers and youth reported on peer victimization. Latent growth curve modeling revealed an increase in effortful engagement responses and a decrease in disengagement and involuntary engagement responses during this period. Peer victimization disrupted these normative trajectories, resulting in less effortful engagement and more effortful disengagement and involuntary stress responses in early adolescence. These findings suggest that early peer victimization sensitizes youth to stress by interfering with the development of effective coping and fostering maladaptive stress responses.