To Wolf’s comments above about not wanting to turn over bank statements etc,.:
I think that Yeshivos and Day Schools should focus on accurately identifying income (true income including gifts from family in exchange for participating in family businesses) and number of children. There is no need to look at expenses — policy should be something like:
Income of X
Allowance of Per Child Expense (maybe age adjusted) of Y
Yields Tuition of Z
If someone agrees to pay Z then fine.
If someone wants to pay less than Z they should need to explain special expenses or circumstances. Otherwise, why should the yeshiva care whether family money is spent on mortgage, meat, internet access, cleaning help or vacation. Let the family decide!