This technical report provides data on the extent to which progress monitoring measures explain reading achievement. The four progress monitoring measures discussed are: letter sounding, phonemic segmentation, oral reading fluency, and comprehension given in either oral or written form. These measures were administered to first grade students in low- and high-income schools. A regression analysis indicated that the Letter Sounding and Phonemic Segmenting tests correlate with each other, as well as the ORF measure, the Listening Comprehension test, and the Constructed Response section of the Reading Comprehension test. However, these measures do not correlate with the Reading Comprehension test. The ORF and Reading Comprehension measures correlated with all other first-grade reading measures. Another important finding was that more students from low-income schools needed to take the Listening Comprehension test rather than the Reading Comprehension test. This finding indicates a potential area of concern for school districts. (Contains 7 tables.)