Table 4. Step-wise school opening online and off-line in Korea during COVID-19 pandemic in 2020.

School opening		Dates	School grades, G
Online
	1st	April 9	G12, G9
	2nd	April 16	G11–10, G8–7, G6–4
	3rd	April 20	G3–1
Off-line
	1st	May 20	G12
	2nd	May 27	G11, G9, G2–1, Kindergarten
	3rd	June 3	G10, G8, G4–3
	4th	June 8	G7, G6–5

In Korean education system, children in G1–G6 are in elementary schools, students in G7–G9 in middle schools, and students in G10–G12 are in high schools.

COVID-19 = coronavirus disease 2019.