Objectives: This study is a foundation for preparing learning support measures for children with developmental language disabilities through research on the academic relationship development of the Korean language and mathematics. The degree and developmental relationship of Korean language and mathematics academic performance according to age from kindergarten before entering elementary school to 4th grade were examined. Methods: Latent Growth Model Analysis (LGMA) was conducted on the results of the evaluation of Korean language and mathematics academic performance from 2014 to 2018 (4th grade in elementary school). Results: Korean language and mathematics developed with significant influence on each other. It was confirmed that the basic ability to perform the Korean language has a significant effect on both the basic ability and the change in the academic ability in mathematics. It is a fact that Korean language ability is the basis of mathematical academic ability through the implementation of the mathematical sentence system. In addition, although Korean language ability and mathematics influence each other, in the case of mathematics, the cognitive ability of individual children played a more significant role compared to the Korean language in the academic performance results. Conclusion: Korean language ability and mathematics developed with a significant influence on each other. It was confirmed through the Latent Growth Model that Korean language ability has a significant effect on the basic ability and the change of mathematic academic performance.