The primary aim of this study was to examine the structure of processing speed (PS) in middle childhood by comparing five theoretically driven models of PS. The models consisted of two conceptual models (a unitary model, a complexity model) and three methodological models (a stimulus material model, an output modality model, and a timing modality model). A second aim was to evaluate the utility of these models for key reading skills (single word reading, fluency, and comprehension) relevant to this age group. Participants consisted of 844 children enrolled in urban public elementary schools. Average participant age was 9.92 (SD = 0.89) and students were enrolled in 3rd (n = 186), 4th (n = 482) and 5th (n = 176) grade. Sixteen variables from 12 tasks differing in their demand characteristics captured PS. Confirmatory factor analyses and regression equations evaluated hypotheses. A two-factor Timing model (Latency and Efficiency) was the strongest fit to the data and similarly structured two-factor Complexity model (Simple and Complex) was also a good fit to the data. Both models were examined as predictors of reading skills. Only the Efficiency/Complex factors were predictive of each key reading skill when considered alone and with relevant language and demographic variables, with the exception of single word reading, where both PS latent factors were predictive in the context of covariates. The structure of PS in middle childhood was found to form a two-factor structure, and separation was apparent between a simpler and more complex level of timed processing. Additionally, PS appears to be contributory to the prediction of word single word reading, reading fluency, and reading comprehension in the context of highly relevant predictors. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]