This study analyzed trends in shadow education participation and disparities by socio-economic status among K-12 students, and drew educational implications based on merged the data from the ‘Shadow Education Expenditure Survey for elementary, middle, and high schools from 2017 to 2022. To do so, regression analyses were conducted with the monthly shadow education expenditure as the dependent variable. In the process, any changes in participation in shadow education before and after 2020, when lock-down measures were tightened due to COVID-19, were noted. The results showed that the average monthly cost of shadow education has been increased and the gap by socio-economic status has been widened. Meanwhile, there was a temporary decrease in the average and the gap of shadow education costs for elementary school students in 2020. In contrast to other school levels, participation in shadow education for child care purposes in addition to learning is common in elementary school. However, when the type of participation in shadow education was limited to knowledge-based subjects for learning purposes, the effect of lock-down measures due to COVID-19 was found to lose statistical significance also in elementary school. The need for a rigorous diagnosis of the widening gap in shadow education participation and the need for different policy approach depending on the type of shadow education participation was discussed.