50% of schools' gas is consumed when they are closed. This is very wasteful and represents the easiest opportunity to save energy by making sure that your boiler is not scheduled to come on at weekends and by having a procedure in place to turn it off before holidays. If there is legitimate usage e.g. community use, then you should ensure only those parts of the building are heated and not the whole school. This is particularly true if a member of staff wants to come in. In almost all circumstances, it is more efficient to ask them to use an electric fan heater just for the area they are working in. Contractors often do physical work and do not generally need the heating to be left on.
If you have 24 hour timers in some building which do not know the day of the week, they should be replaced by seven day timers to avoid heating being left on at weekends.