This study aims to identify changes in core competencies according to the economic background of middle school students in Gyeonggi-do before and after COVID-19 and to explore the factors influencing this change. To this end, this study explores changes in competency gap by economic situation of families before and after COVID-19 and in the competency level by student as well as the factors that influence school competency level. The result indicates that the higher the monthly income of a household, the higher the tendency to increase cognitive ability in 2021 (after COVID-19) instead of in 2018 (before COVID-19). Examining the change in the competency level of schools before and after COVID-19, the difference in school improvement was the largest in the case of cognitive competency, followed by autonomous and social competencies. At student level, reading activities, intrinsic motivation levels, self-directed learning tendencies, and positive companionships positively influenced the competency level of the school. In addition, the higher the degree of remote classes centered on teacher-recorded videos in schools, the greater the degree of decline in social competence before and after COVID-19 or the lower the degree of improvement. Therefore, actively responding to the competency gap between income classes, which deepened due to COVID-19, and establishing practical school education measures for cultivating social, autonomous, and cognitive competencies are necessary initiatives.