Previous research suggests that multiple representations can improve science reading comprehension. This facilitation effect is premised on the observation that readers can efficiently integrate information in text and diagram formats; however, this effect in young readers is still contested. Using eye-tracking technology and sequential analysis, this study investigated students' reading strategies and comprehension of illustrated biology texts in relation to adult readers' performance. The target population was fourth-grade students with high reading ability, and the control group was university students. All participants read a biology article from an elementary school science textbook containing two illustrations, one representational and one decorative. After the reading task, participants answered questions on recognition, textual, and illustration items. Unsurprisingly, the university students outperformed the younger students on all tests; however, more interestingly, eye movement patterns differed across the two groups. The adult readers demonstrated bidirectional reading pathways for both text and illustrations, whereas the fourth graders' eye fixations only went back and forth within paragraphs in the text and between the illustrations, but made fewer references to both text and illustration. This suggests that regardless of their high reading ability, fourth-grade students' visual literacy is not mature enough to perceive connections between corresponding features of different representations crucial to reading comprehension. Despite differences in cognitive processes between adult readers and young readers, high-ability young readers still have certain capabilities in reading comprehension. The results of sequential analysis showed that they looked back to previous paragraphs frequently, indicating that they were monitoring their comprehension.