<p>The present study investigated the directionality of the relations of reading with science and social studies domain knowledge from fourth through seventh grade in Korean students, an underrepresented sample in reading research. We analyzed Jeonnam Educational Longitudinal Study Panel 1 by using the Random-Intercept Cross-Lagged Panel Model. The study replicated the positive bidirectional relation between science domain knowledge and reading, suggesting that the reciprocal relation extends beyond elementary years. Notably, this study provides the first evidence demonstrating a positive bidirectional relation between social studies domain knowledge and reading. Moreover, to explore potential domain-specific differences, we compared the trajectories of domain knowledge development in relation to reading development by domain. The results revealed the dynamic nature of the reciprocal relation between domain knowledge and reading. Whereas the role of reading in predicting knowledge development was consistent across both domains, the role of social studies domain knowledge in predicting subsequent reading was more pronounced, compared to that of science domain knowledge in a time point from fourth to fifth grade. Collectively, the results highlight the importance of simultaneously supporting reading and domain knowledge of science and social studies.</p>