In this study we measured event-related potentials (ERPs) and evoked heart rate (EHR) to investigate performance monitoring in 10-12-year-old children. The children received feedback on their performance while conducting a probabilistic learning task. Error-related ERP components time-locked to the response increased in amplitude when the children had learned the task, whereas the feedback-locked components decreased. Concerning EHR, there was a general reduction in feedback-related heart rate deceleration when the children had learned. Moreover, a prolonged heart rate deceleration was observed at negative feedback onset in comparison to positive feedback, which shifted in timing when the task progressed. Together, the ERP and EHR-measures suggest a shift from external to internal monitoring when the children are learning by performance feedback. The data suggest that error- and feedback-related EHR deceleration is a reflection of the same error monitoring system that is responsible for the emergence of the error-related negativity (ERN).