Jung Jieun This study longitudinally explored the developmental patterns of middle school students’ reading ability and reading motivation using latent transfer analysis. The key findings are as follows: First, reading abilitydevelopment did not progress uniformly across genders, with girls developing faster than boys. Second, reading motivation qualitatively varied with increasing grade level, depending on self-determination. In- ternal regulation and integrated, identified, and introjected regulation de- creased, while external regulation and no regulation tended to increase. Third, model fit testing revealed that a three-latent group model was the most appropriate for both T1 and T2. Fourth, nine groups were identified through group transition probabilities and patterns across time periods, demonstrating that reading ability and reading motivation interact to shape diverse developmental trajectories.