I dont agree,
the problem with schools is that the frequency is always terrible , if you are lucky you get a 6 monthly with schools but usually once a year if that.
Why waste all that time in wfp'ing, waiting for windows to dry then checking for runs , then doing them again / glass only / wiping runs or spots with scrim etc.
I say WFP glass only upstairs and trad downstairs nice and quick , get your money and come back when they are filthy once more and do the same,
IF and its a big IF the school is quarterly or better frequency then i agree to wfp the whole lot, though i bet the frequency is not regular and will make little or no difference to your annual turnover, hence dont waste your valuable time!