This study evaluated the validity of a new scale for assessing children's reading fluency skill called the Comprehensive Oral Reading Fluency Scale (CORFS). The CORFS consists of two subscales that capture key elements of the Kuhn, Schwanenflugel, and Meisinger (2010) definition of reading fluency: reading expression, reading rate, and accuracy. In study 1, the reading expression subscale was developed by examining spectrographically measured prosodic differences in the oral readings of children with varying fluency skill. Three experts independently rated the oral readings of 59 second-grade children using the CORFS. Intraclass correlations among raters were strong for both reading expression, and reading rate and accuracy. Expression ratings correlated with all but one spectrographic indicator of reading prosody and highly with standardized assessments of reading fluency and comprehension. In study 2, the structure of the scale was replicated using spectrographic measures of the oral readings of 60 third-grade children reading two new texts. Two experts independently rated these oral readings using a final version of the scale. Results were comparable to those of study 1. Together, these results support the validity of the CORFS as an assessment of reading fluency. (Contains 1 figure and 13 tables.)