We used data derived from a survey sample, the Connecticut Longitudinal Study (CLS), to compare two commonly employed definitions of reading disability: a discrepancy-based model (D) and a low reading achievement model (L). We identified children satisfying each definition in second grade and compared the groups retrospectively in kindergarten and prospectively in fifth grade using parent-based, teacher-based, and child-based measures. Our findings suggest more similarities than differences between the reading disabled groups. The most salient differences were those related to ability and seem inherent in the definitions of the groups: Children identified as D have significantly higher verbal, performance, and full scale IQ scores than those identified as L. These findings suggest that both groups of children with reading disability, that is, those defined by either D or L, should be considered eligible for special education services.