The purpose of this study was to investigate differences between readers with different levels of comprehension skill when engaging in a causal questioning activity during reading, and the varied effects on inference generation. Fourth-grade readers (n = 74) with different levels of comprehension skill read narrative texts aloud and were asked causal questions at specific points during reading. Responses to questions were examined for the types of inferences the readers made during reading. There was no main effect of comprehension skill in terms of readers' text-based inferences made in response to the causal questions. However, readers differed in their use of knowledge-based inferences in response to the causal questions, and in particular knowledge-based inferences that connected to related text information. Results are discussed in terms of individual differences that can influence attempts at maintaining coherence during reading.