<p>Understanding the factors that influence students’ math achievement is a crucial area of research in the educational field, given the significance of mathematics in shaping students’ academic and professional futures. This study focuses on examining the predictive effect of learning strategies, learning attitudes, and self-efficacy on math achievement at both the student and school levels among ninth-grade students in South Korea. The study also investigates cross-level interaction to better understand the multilevel nature of learning processes. Using a two-level hierarchical linear model, the study analyzed the 2017 GEPS’s six waves of panel data, with a total sample size of 5311 9th grade students. The results indicate that students’ learning strategies, learning attitudes, and self-efficacy in math are significant predictors of math achievement. The study also found a positive school contextual effect of self-efficacy in math learning on math achievement. Additionally, the positive cross-level moderating effect suggests that as the school mean self-efficacy value increases, the relationship between an individual’s self-efficacy in math and math achievement becomes stronger. The findings of this study provide valuable insights into the functioning of self-efficacy in math learning among South Korean 9th grade students, while taking into account the school context.</p>