Using electroencephalographic recordings (EEG), we assessed differences in oscillatory cortical activity during auditory-oddball performance between children aged 9-13 years, younger adults, and older adults. From childhood to old age, phase synchronization increased within and between electrodes, whereas whole power and evoked power decreased. We conclude that the cortical dynamics of perceptual processing undergo substantial reorganization from childhood to old age, and discuss possible reasons for the inverse relation between age trends in phase synchronization and power, such as lifespan differences in neural background activity, or a lifespan shift from rate coding in children to temporal coding in adults.