This study investigated early adolescents' psychophysiological response to a school-related stressor (SRS) as indexed by heart rate variability and examined the unique and interactive effects of heart rate variability and temperament on academic achievement. A total of 91 seventh graders watched an SRS video-clip while their heart rate variability was registered. Temperament and grades were also assessed. Heart rate variability decreased from baseline while watching the video-clip, indicating the activation of a stress response, and returned to basal level when recovering. Regression analyses revealed that among youth with an inhibited temperament, higher heart rate variability in the poststressor phase was related to better performance, whereas socially outgoing students performed well regardless of their recovery rate. These are among the first data to report on the link between early adolescents' parasympathetic self-regulatory activity in response to an SRS, temperamental profiles, and academic functioning. Implications for theory and educational practice are discussed.