This study explored characteristics of reading comprehension difficulties among Chinese students learning English as a second language (ESL). Two hundred forty-six Grade 8 English-immersion students in China were administered a battery of reading-related and reading comprehension tests. Three groups of comprehenders matched on age, nonverbal intelligence, and word-reading speed were identified: unexpected poor comprehenders, expected average comprehenders, and unexpected good comprehenders. The three groups differed in vocabulary and higher level processes. Vocabulary breadth and depth distinguished between the unexpected poor comprehenders and the expected average comprehenders. Inference, strategy, listening comprehension, summary writing, and morphological awareness distinguished between the expected average comprehenders and the unexpected good comprehenders. The findings suggest that vocabulary is the main source of reading comprehension difficulties in ESL unexpected poor comprehenders. The advantage of the unexpected good comprehenders group is primarily due to discourse comprehension and strategic processes, and is only possible with high language proficiency. There is no evidence that ESL unexpected poor comprehenders have poor Chinese (L1) reading ability.