This study investigated how measures of decoding, fluency, and comprehension in middle school students overlap with one another, whether the pattern of overlap differs between struggling and typical readers, and the relative frequency of different types of reading difficulties. The 1,748 sixth, seventh, and eighth grade students were oversampled for struggling readers (n = 1,025) on the basis of the state reading comprehension proficiency measure. Multigroup confirmatory factor analyses showed partial invariance among struggling and typical readers (with differential loadings for fluency and for comprehension), and strict invariance for decoding and a combined fluency/comprehension factor. Among these struggling readers, most (85%) also had weaknesses on nationally standardized measures, particularly in comprehension; however, most of these also had difficulties in decoding or fluency. These results show that the number of students with a specific comprehension problem is lower than recent consensus reports estimate and that the relation of different reading components varies according to struggling versus proficient readers.