hi we do a school once a year, I always before I price ask if they will be taking down posters, drawings etc, I tell them if they clear the windows they will get a better price, mine is a medium size infant school and I charge £280, we wfp outside and pole/wagtail the inside, takes me a day, don't equate it to the headmasters house as thats his own money he pays you with, he won't personally be paying for the school so charge accordingly, if your unsure how to price go and test clean a window and time it then do the maths, hope this helps
graham