With the current setup, if your default due date for charges is set to the 1st of the month, then when a charge is entered on the 15th the default due date is before it was charged.
Yes, it can be changed manually, but this requires human intervention which is not a good thing to rely on and adds another step to charge processing.
A default due date of "x days from date of charge" would be appropriate for organizations with a "due in 30 days" policy. I don't think I've ever met a policy which specifies that all charges will be due on a specific day of the month, which is the current setup. Due dates are generally relative to the charge date.
It would also improve the parent experience, and not provide A/R information that is out of line with school policy.
The current setup doesn't even allow setting a default due date of the 30th, because the options only go up to the 28th (as not all months go to the 30th).
If "x days from date of charge" accepted "0 days", this would also cover organizations where charges are due the date they are charged.
The setup for due date field should be First Day, Last Day, specific date (date can be entered) of the current or next month instead of a listing of numbers from 1st to 28th.