Objective: This study investigated which Rapid Automatized Naming (RAN) tasks (i.e., letters and digits) are most predictive of reading fluency, and whether RAN predicts variance in reading fluency beyond general processing speed. It is hypothesized that alphanumeric RAN tasks will better explain individual differences in reading fluency performance than general processing speed. Method: 64 clinic-referred children from a reading clinic were selected as the participants for this study. Participants included males and females aged 7.25 years to 15.5 years (M = 10). Only participants whose fluency performance scores were average or below were included in the final analyses. Participants in this study were administered a battery of tests that included reliable measures of RAN, phonemic awareness, general processing speed, and reading fluency. Results: The results suggest that alphanumeric RAN task performance, and letter naming in particular, are unique contributors to reading fluency performance in dysfluent readers. Although previous research has demonstrated that generalized processing speed is associated with RAN performance, it cannot account for the relationship between RAN and reading fluency in this sample. Conclusion(s): The findings revealed different patterns of results for naming speed for letter and digit naming speed in children of this age. Alphanumeric naming speed, and especially letter naming, better assess an underlying phonological processing ability that is common to fluent reading. Assessment professionals should consider the results of this study when selecting instruments to identify fluency-based reading difficulties.