This study examined how students' motivational regulation affects their academic performance based on the self-determination theory (SDT). The research involved data analysis from over 7,056 sixth-grade students in 446 South Korean elementary schools. We applied a stepwise multi-level modeling (MLM) approach to assess the influence of five self-determined motivational regulation impacts (i.e., amotivation, external regulation, introjected regulation, identified regulation, and intrinsic regulation) on students' literacy and math achievements. Additionally, we considered environmental differences among schools, including the type of school (i.e., public or private) and locations (i.e., urban, suburban, or rural). The study highlights the importance of fostering perceived identified regulation to enhance academic achievement in elementary students. The findings indicate that students tend to show higher academic achievement when they recognize the value of their learning experiences and that their complex motivational regulation patterns can be more thoroughly understood by considering cultural and environmental factors.