I don't have the figures to hand here at the moment. But basically: very few UK schools have sprinkler systems, but of the systems that exist, they will most be full systems (as that is the only system that will give you any insurance discount) and therefore will have heads everywhere.
As for fears of total deluge - at risk of going round in circles, sprinkler heads only operate where there is a fire.
As for costs, this has been discussed before, but briefly cost benefit calculation taking into account massive insurnace premium savings, building design trade offs (at risk of offended whom ever didn't like me saying "trade off") and the fact that 99% of the time (BASA figures) they put the fire out without any assistance, I'd say it pays to install them.
