Movement sensors can work well in rooms with occasional use such as toilets, photocopier and resource rooms and store cupboards. They can be installed on existing lights or included in new light fittings when fittings are replaced. You can either get an electrical contractor to do this for existing lights or make sure it's added to the requirements if light fittings are being replaced en masse.
In the short term, the most effective way to reduce lighting usage in unoccupied rooms is to ask staff and pupils to switch the lights off manually. Energy Sparks has a number of pupil activities, for example carrying out spot checks at lunch, to help with this. If pupils and staff do this on an ongoing basis, it often works better than paying to install occupancy sensors. You should also ask cleaning staff to turn off lights as they clean the building. High early morning or late evening usage often indicates that energy is being wasted because cleaners turn on lights as they go through the school and leave it to the caretaker to turn them off afterwards.