Because WKSK only has 7 classrooms, K1 and K2 each has 3 AM and 3 PM in 6 classrooms every year. K1 and K2 take turns to share the remaining classroom (7th) in AM and PM.
For example:
This year, 7th classroom is K1 AM and K2 PM.
Next year, 7th classroom will be K2 AM and K1 PM.