we have some special schools in our county (Gloucestershire) that use key operated break glass units i.e. no glass just a key switch. The children have behaviour problems and will always tamper with conventional units even if they have a protective lid/seal. See link below for example:
http://www.fulleon.co.uk.../KeySwitchCallPoint.html
All staff carry a key and will operate the call point in the event of fire. This is acceptable under fire risk assessment. If your units are conventional and you are just using the test key this may not be acceptable as the glass will likely have been removed and sometimes it is awkward and diificult to get the test keys in. I would get the units changed out to the above type as they meet all approvals.

I am not particularly comfortable with the idea of fiddling around with School MCPs where bad behaviour has led to unwanted fire signals (UwFS). In general terms, these are often the premises where arson is more likely, so to reduce - or remove- such a control measure could be seen as a little iffy

For mental health and other special circumstances, it may be justifiable - but unless there are sufficient staff (key holders) circulating the School, how are the pupils supposed to raise the alarm if there is a genuine fire? Would there be sufficient staff- say at lunchtime - or would they all be filling their faces in the staff room?

I worked on a project in a college which has severe UwFS problems. The solution was to alter the MCPs, so they had alarmed covers AND only sounded an alarm in the School office which was always occupied when thee college was open. using a time delay system, staff then had 4 minutes to investigate and report back to the office.

It has stopped most, but not all UwFS's, as some students love the idea of staff having to run around the building. But the fire service is no longer called, or the building evacuated - so disruption is minimal.

The response procedure has been recorded as a variation from BS589-1 in the FRA and agreed with the local fire bobbies (enforcement team). After all, London Underground use this system in deep underground stations full of 1000s of passengers, so to use a similar system (backed up with the correct procedure and training) should be suitable for a two storey School with a few hundred kids!!