Scientific texts are often multimodal, consisting of both text and illustrations. However, previous research indicates that young readers are poor at using text-and-illustration integration strategies and at in-depth processing of scientific illustration information. This study used an experimental paradigm to teach strategies of illustration reading and text-and-illustration integration to fourth-grade students. The study manipulated reading ability (high vs. low level) and teaching strategy (presence vs. absence of reading strategies instruction) as between-subjects variables. Seventy-one participants completed a prior-knowledge test, read two illustrated biology texts, and answered comprehension questions. The results showed that the instructed groups outperformed the control groups on the overall reading test, and in the illustration memory and integration items. It was inspiring to discover that teaching fourth-grade students of both high and low reading ability levels to pay attention to scientific illustrations, process them in-depth, and consider the relationship between textual descriptions and detailed parts of illustrations benefited these young readers in reading comprehension and acquiring scientific knowledge.