Explicit reading strategies help low-knowledge readers make the inferences necessary to comprehend expository texts. Self-explanation is a particularly effective strategy, but it is challenging to monitor how well a reader is applying self-explanation without requiring the reader to externalise the self-explanations being generated. Studies have shown that different reading strategies vary in the amount of cognitive control required as well as the engagement of brain regions involved in internally-directed attention. Pupil diameter is related to task engagement and cognitive control via the brain's locus coeruleus-norepinephrine system. Therefore, pupil diameter could be a method to unobtrusively measure a reader's use of self-explanation. The current study assessed whether pupil diameter can be used to distinguish between the use of different reading strategies and whether it is linked to the quality and effectiveness of the strategy in terms of learning gains. Participants reread, paraphrased, and self-explained texts while pupil diameter was recorded, and completed comprehension tests. Average pupil diameter differed between all three reading strategies, and pupil diameter was related to learning gains and the quality of strategy use. The results suggest that pupil diameter could be used to track effective reading strategy utilisation.