To compare the pattern and distribution of event-related potential (ERP) N270 in adults and school-age children and to explore the development of conflict processing systems in the human brain, pairs of colored numbers were sequentially presented on a screen to subjects. The subjects were instructed to discriminate whether the color or magnitude of the pairs of numbers were identical (match) or different (conflict), and ERPs were recorded at the same time. In adults, a negative potential peaking at 270 ms (N270) was elicited when the second stimulus (S2) conflicted with the first stimulus (S1) in either task relevant or irrelevant conditions. N270 was distributed widely on the scalp in adults. In children, N270 was only elicited by a task-relevant conflict. N270 in the color conflict was distributed bilaterally on the scalp and N270 elicited by the magnitude conflict was found to be on the left central-frontal areas. In school-age children, ERP N270 is elicited under the control of attention. Its distribution on the scalp depends on the attributes of stimulus pairs. (C) 2003 Elsevier Science B.V. All rights reserved.