Don't know if it's the same everywhere, but certainly round here, the schools have their own budgets for window cleaning, and it doesn't appear to be high on the agenda! We cleaned a few in the summer, which hadn't been done for a few years, one which hadn't been done in 5!!
Money was ok, not amazing, but, payment was exceptional, which anyone dealing with commercial clients, will know that it's nice not to chase or worry.
We clean 3 private schools on a quarterly basis, payments are prompt and work is well paid.
Not much of a conclusion for you, I know, other than they pay promptly!