Purpose: The objective of this study was to assess and compare the predictive values of group membership for rapid automatized naming (RAN) and phonemic awareness (PA) in Dutch school children with and without reading disabilities (RD) or specific language impairment (SLI). Method: A composite word reading index and a formal SLI diagnosis were used to classify a total of 1,267 children aged 8 to 13 years old either as RD-only ( n = 126), SLI-only ( n = 21), comorbid (RD+SLI; n = 30), or typically developing ( n = 1,090). RAN and PA were assessed with 4 standardized subtests. The clinical subgroups were compared to each other and contrasted with the control group. Results: For each subgroup, results indicate substantial effect sizes of RAN and PA. However, the RD-only group seems to be more affected by poor RAN than the SLI-only group, whereas the 2 groups perform equally poorly on PA. The comorbid group was revealed as most severely impaired on all measurements. Conclusions: In studying RD and SLI, this research indicates that it is important to distinguish between RD-only, SLI-only, and comorbid groups. The comorbid group shows additive effects of both disorders.