Reading is a critical skill as it provides a gateway for other learning within and outside of school. Many children struggle to acquire this fundamental skill. Suboptimal design of books for beginning readers may be one factor that contributes to the difficulties children experience. Specifically, extraneous details in illustrations (i.e., interesting but irrelevant to the story elements) could promote attentional competition and hamper emerging literacy skills. We used eye-tracking technology to examine this possibility. The results of this study indicated that excluding extraneous details from illustrations in a book for beginning readers reduced attentional competition (indexed by gaze shifts away from text) and improved children's reading comprehension. This study suggests that design of reading materials for children learning to read can be optimized to promote literacy development in children. [This paper was published in: "Proceedings of the 40th Annual Conference of the Cognitive Science Society," 2018, pp. 336-41.]