This study used the modality shift experiment, a relatively simple reaction time measure to visual and auditory stimuli, to examine attentional shifting within and across modalities in 33 children and 42 adults with high-functioning autism as compared to matched numbers of age- and ability-matched typical controls. An exaggerated "modality shift effect" relative to the TD children occurred for the children with autism in conditions involving the reaction time when shifting from sound to light but not from light to sound. No exaggerated MSE was found for the adults with autism; rather, their responses were characterized by a generalized slowness relative to the adults with TD. These results suggest a lag in maturational development in autism in basic information processing mechanisms.