The purpose of this study was to identify students at risk of reading comprehension difficulties by using the responsiveness to intervention (RTI) approach. The participants were 177 students in Grades 1-3 in three elementary schools in South Korea. The students received Tier 1 instruction of RTI from March to May 2011, and their performance was measured using a curriculum-based measurement, the BASA-Maze, at monthly intervals. Latent class growth analysis was employed to analyze the data. Results identified four empirically distinct classes for the first grade and five such classes for the second and third grades. Additionally, students were classified into groups of those who need (i.e., at-risk students) and those who do not need Tier 2 instructions for reading comprehension in each grade. The importance of RTI and the critical role of progress monitoring for early identification of comprehension difficulties were discussed, and suggestions for future research were provided.