In a competition-driven meritocratic learning environment, academic achievement can have a direct effect on self-esteem and self-concept. As such, academic achievement can act as an antecedent to grit and self-esteem. This study examined the longitudinal reciprocal relationships of academic achievement, consistency of interest (CI), perseverance of effort (PE), and self-esteem among fourth-grade and fifth-grade primary school students in South Korea, who were under heavy pressure in a performance-oriented learning environment. Data pertaining to 2,240 students were extracted from the 2018 Korean Children and Youth Panel Survey conducted by the National Youth Policy Institute, and cross-lagged structural equation modeling was conducted to examine the longitudinal relationship between three variables. The results revealed that academic achievement had a statistically significant positive relationship with CI, PE, and self-esteem; CI had a statistically significant positive relationship with PE; and PE had a statistically significant positive relationship with self-esteem through the mediation of academic achievement. In addition, self-esteem demonstrated the highest level of stability, and although CI and PE demonstrated similar levels of stability, CI displayed slightly greater stability compared to PE. Findings from this study suggest the need to support grit and self-esteem among Korean students under pressure in performance-oriented academic environments.