Being not far off is not the same as being correct. No doubt unions and parents would like it to be a teacher in front of every class, emergencies excepted, but this is not the case. A combination of teacher shortages, supply teacher shortages and financial constraints have led to the situation being as Meoir Shee has explained. If a teacher is not available because of exam administration, jury service(!), illness, duties as a teacher governor, being away on interview, attending child protection meetings, compulsory training, sickness or whatever, it is more than likely that a cover supervisor will be in charge.