Dyslexic children are probably not a homogeneous group in terms of important characteristics assumed to be involved in reading; disability since underlying causes may vary widely. Such characteristics as arousal and performance on a vigilance task would differ not only from a control group, but also within the RD sample. It was hypothesized that HBD symptoms would be associated with lowered arousal and poorer vigilance performance whereas children experiencing reading difficulties presumably because of specific language dysfunction would resemble controls in arousal and performance. The results supported vigilance predictions for omissions, but not commissions. Poorer performance was associated with HBD symptoms. Age, however, proved to have an even greater effect on vigilance performance. Arousal results, for the most part, were not in the predicted direction. Arousal, measured by skin conductance, increased over time for children in this sample, rather than decreased as we expected from adult data. This indicated that vigilance and arousal cannot be equated in the same sense that has been suggested for adults.