Some children demonstrate adequate or better reading achievement in early school grades but fall significantly behind their peers in later grades. These children are often referred to as late-emerging poor readers. In this study, we investigated the prevalence and heterogeneity of these poor readers. We also examined the early language and nonverbal cognitive abilities of late-emerging poor readers. Participants were 493 children who were a subsample from an epidemiological study of language impairments in school-age children. In kindergarten, children were administered a battery of language, early literacy, and nonverbal cognitive measures. Word reading and reading comprehension achievement was assessed in 2nd, 4th, 8th, and tenth grades. Latent transition analysis was used to model changes in reading classification (good vs. poor reader) across grades. Population estimates revealed that 13.4% of children could be classified as late-emerging poor readers. These children could be divided into those with problems in comprehension alone (52%), word reading alone (36%), or both (12%). Further results indicated that late-emerging poor readers often had a history of language and/or nonverbal cognitive impairments in kindergarten. Subtypes of poor readers also differed significantly in their profiles of language, early literacy, and nonverbal cognitive abilities in kindergarten. Results are discussed in terms of causal factors and implications for early identification. (Contains 10 tables, 2 footnotes, and 1 figure.)