For Years 4-12, teachers who cover classes should teach their own subject. For example, if a Science teacher is absent and their lesson is covered by a Mathematics teacher, the colleague should teach Mathematics (during the Science period). When repaying this ‘owed’ period the Science teacher will teach Science during the colleague’s Mathematics period. Effectively, no learning time is lost by students.
When a teacher is absent the school does not arrange a ‘supply’ or ‘casual’ teacher like in western countries. Rather, colleagues who teach the same class/es will be asked to cover the absent teacher’s lessons during that day. The teacher who is absent will (in most cases) then ‘owe’ the colleagues periods who covered classes for them while they were absent. The periods owed do not have to be repaid immediately but should be repaid within each school term.