Objective: Research suggests that Cognitive Efficiency (CE) is a distinct factor important to the development of reading fluency (RF) skills, however, it is not well established which component(s) of CE are most predictive of RF in children. This study investigates which components of CE (working memory and processing speed) are most predictive of RF, and if CE accounts for unique variance in RF beyond other well-established predictors of reading (phonemic awareness). Method: 130 school-referred subjects, with equal numbers of male and female students ranging in age from 7 to 16 years (M = 10), were administered tests from the Woodcock-Johnson III. The battery consisted of measures of verbal ability, phonemic awareness, processing speed, working memory, and RF. Children with IQ's below 80 were not included. Results: Hierarchical multiple regression analysis results indicated a significant relationship, accounting for 25% of the variance between processing speed and RF, that is independent of other cognitive factors (p < .001). Results did not find a significant relationship between measures of working memory and RF in this sample. Conclusion(s): Findings suggest that the processing speed component of CE is the most significant contributor of RF in this sample. The findings further suggest that this relationship extends beyond what is explained by verbal ability and phonemic awareness. Moreover, a composite score CE does not better predict RF over a single measure of processing speed.