This study examined the sources of reading comprehension difficulties in English language learners (ELLs). The characteristics of ELL poor comprehenders were compared to their English as a first language (EL1) peers. Participants included 124 ELLs who spoke Chinese as an L1 and 79 EL1 students. Using a regression technique based on age, non-verbal reasoning, word reading accuracy, and word reading fluency, three types of comprehenders (poor, average, and good) were identified within each language group. The groups were then compared on measures of oral language skills (vocabulary breadth, vocabulary depth, and listening comprehension), metalinguistic skills (morphological awareness and syntactic awareness), working memory, and higher-level processing skills (inference, conjunction use, and comprehension monitoring). ELL poor comprehenders had significantly lower scores than ELL average and good comprehenders on vocabulary breadth, listening comprehension, and morphological awareness, whereas there were no significant differences between the average and good comprehender groups on these skills. Additionally, both ELL poor and average comprehenders had lower scores than ELL good comprehenders on all three higher-level skills. Finally, results showed that ELL poor comprehenders scored lower than EL1 poor comprehenders on vocabulary breadth, listening comprehension, and morphological awareness, but the two groups did not differ on higher-level skills. Theoretical and educational implications for the identification and instruction of ELL poor comprehenders are discussed.