This study evaluated how measures of oral reading fluency (ORF) and silent reading fluency (SRF) compare as predictors of reading comprehension and how these predictors vary as a function of proficiency level for fourth- and fifth-grade students. Additionally, the study sought to examine the relationship between measures of oral reading fluency, silent reading fluency, reading comprehension, and the Transitional Colorado Assessment Program (TCAP) with these students. Participants were 175 fourth- and fifth-grade students from two randomly selected schools in Colorado. A correlational predictive design was used. Results indicated that measures of ORF and SRF were predictors of reading comprehension and that the relationship of measures of ORF and SRF with comprehension changes over time. Regression analysis results indicated that 45.0% of the variance in reading comprehension was accounted for by the ORF measure for the sample population, as compared to 53.0% of the variance accounted for by SRF measures. Thus, measures of SRF might be a better predictor for maturing readers to determine reading proficiency, monitor student progress, and guide instructional practices. A structural equation model (SEM) analyzed the relationship of the measure of SRF with reading comprehension as moderated by proficiency level. Analysis for the SRF measure by reading proficiency was conducted at the whole group level. The model accounted for 59.0% of the moderation. Results indicated that reading proficiency level and the SRF measure were both associated with reading comprehension. Reading proficiency level is a significant moderator of the relationship between measures of reading comprehension and SRF. A SEM mediation model was used to analyze the relationship of measures of ORF, SRF, reading comprehension, and TCAP. The direct effects of the ORF and SRF measures on TCAP were both predictive with 66.0% of the variance accounted for with SRF measure and 66.5% of the variance accounted for with ORF measure. Results indicated that as grade level increases, the relationship between measures of ORF, SRF, and reading comprehension changes. Additionally, SRF measures can be a viable alternative to ORF measures for upper elementary students as a predictor of reading comprehension and on the TCAP high-stake assessment.