Payment by results is problematic, especially for schools in areas with social deprivation
Yes, but also vice versa - a great school in a wealthy area might just have thick kids, especially if the area becomes fashionable with wealthy buraki.
That's been suggested before and dismissed as unworkable.
Someone tried it with me once. I agreed, but on condition that I had full freedom to conduct the classes as I saw fit, without external interference. I especially pointed out that payment on results meant that I no longer agreed to allow kids to attend the stupid 'rekolacja' in the middle of the school day, and that any kids off sick would be expected to return the school completely prepared and caught up on their missed work.
The idea was quickly dropped.