The purpose of this study is to examine how proportional reasoning is introduced and developed in two widely used U.S. and Korean mathematics textbooks for grades 6-7. Seven research-based frameworks that identify student learning opportunities for understanding of proportional reasoning were used to analyze the textbooks. The results showed that American textbooks include more problems that require explanations and make use of more effective contextual and number structure of problems than Korean textbooks. In contrast, Korean textbooks make a shift from providing highly contextualized problems to presenting abstract and purely computational problems, which aligns with the process of concreteness fading. In addition, Korean textbooks contain more unique types of topics and representations. [For the complete proceedings, see ED630210.]