This study examined the degree to which core reading-related latent constructs, such as reading comprehension, language comprehension, word decoding, non-word decoding, phonological awareness, and speed, are equivalent and reflective of the same underlying constructs across different age groups of poor readers. Within this framework, we also worked to better understand whether poor readers at different ages are similar or different in their pattern of relationships among core reading-related constructs. The sample was poor readers at different ages, including 430 elementary students, 584 middle school students and 236 adults. Using confirmatory factor analysis, four models of reading were tested for each age group. Different models of reading were found to best represent reading-related skill across the three groups of poor readers. Specifically, for the elementary school students, reading-related skills were highly correlated and reading skills were best represented by a two-factor model, including the factors of literacy and language comprehension. For the middle school students, latent correlations between reading-related skills were lower than the elementary students and the best fitting model was the four-factor model, including factors of decoding, reading comprehension, speed, and language comprehension. Lastly, reading-related skills for the adult sample were best represented by the six-factor model, including distinct factors of phonological awareness, non-word decoding, word decoding, reading comprehension, speed, and language comprehension.