Mathematics learning is not only determined by mathematical contents, but also by reading strategies that students apply to comprehend the mathematical tasks. Although studies in mathematics education have shown that reading strategies are positively related to mathematics learning, the relation may not be linear as widely believed. Recent research in language assessment has found that the association between reading strategies and reading performance fluctuates as language proficiency increases, a pattern metaphorically called the Island Ridge Curve (IRC). Inspired by the IRC, we hypothesize that the relation between reading strategies and mathematics learning also fluctuates in the pattern of the IRC as students' reading proficiency increases. To verify this assumption, we used a public dataset of 529,091 15-year-old students (M = 15.79, SD = 0.29) from 77 countries/territories. Results of multilevel mixture regression analysis indicated that reading strategies (in our case, understanding and memorizing strategies) are related to mathematics learning through reading proficiency and this relation fluctuates like the IRC. Implications for applying IRC to reading strategies instruction in mathematics education are discussed. (170 words).