The purpose of this study was to discuss music education in the post-COVID-19 era based on the comparison of the results of the 2015 and 2021 Korea Test of Music Cognition(KTMC) of sixth graders at Seoul A School. The subjects of analysis are the results of 478 copies conducted at the same school and the same grade with a 6-year time difference. The conclusions of this study are as follows. First, as a result of comparing the average (M) in 2015 and 2021, it was found to be lower. Second, the average score of each sub-area (tonal, rhythm, and melodic lines) was also lower in 2021 than in 2015. Third, as a result of comparing the standard deviation (SD) in the test results, the standard deviation in 2021 was lower than in 2015. Overall, the music cognitive ability of sixth graders at Seoul A Elementary School, which was examined by the Korea Test of Music Cognition(KTMC), was slightly lower in 2021 than in 2015, and the variation in music cognitive ability between students decreased. This study raised the possibility that students' music cognitive ability may have decreased somewhat after the COVID-19 period. It will be necessary to develop educational materials and curricula to recover this, and it is necessary to find ways to apply them to music subjects by utilizing the advantages of online classes.