Error monitoring allows us to adapt to an inherently dynamic environment. Error monitoring relies mainly on the anterior cingulate cortex (ACC). Its protracted maturation suggests a window for experience-dependent plasticity. To investigate this possibility, we measured error-related response-locked potentials components with morphometric magnetic resonance imaging (MRI) measures of the ACC in twenty-six schoolchildren, aged 6-12 years, enrolled in either a Montessori or a traditional curriculum. We show that the caudal ACC undergoes significant morphometric changes during this age range that relate to error detection ERP activity. Furthermore, pedagogy modulates source localization activity related to error detection within the caudal ACC amongst others. We provide early evidence for a window of opportunity regarding the acquisition of error monitoring skills, with implications for educational practices.