To study age-related changes in cognitive control, event-related potentials (ERPs) of children aged 6-9 years, 10-12 years, and young adults were recorded during a Flanker task. Younger children were more susceptible to conflict than older ones and adults. The N2 in incongruent trials was smaller in younger than older children, who did not differ from adults. The error-related negativity (ERN) following errors, however, was larger in adults than in children, but did not differ between younger and older children. Delayed development of neural responses to error processing relative to conflict monitoring may indicate dissociable maturational time tables of subdivisions of the anterior cingulate cortex.