Heart rate was recorded from five different groups of children (ages 7, 10, 12, 14, and 20 years) while they were performing an auditory selective attention task. The participants were instructed to count rare tone pips embedded in a series of standard tone pips presented at one (attended) ear while ignoring rare and standard stimuli presented at the other (unattended) ear. A pattern of anticipatory heart rate deceleration followed by acceleration was associated with rare tone pips at the attended ear but not with rare tone pips that should be ignored. The absence of differential sensitivity of heart rate responses to rare tone pips presented at the unattended ear was observed for all age groups. These findings were interpreted to suggest that the ability to ignore irrelevant target stimuli has reached mature levels during middle childhood. The depth of anticipatory deceleration increased until age 14, suggesting that the ability to maintain attentional set continues to develop beyond childhood.