When parents are making a payment online, give them the option to select both their "Pay my Past Due Amount" and "Pay my Balance Due" to bring their account current.
If nothing else, there is an opportunity to make it more clear to parents that just paying the Balance Due does not necessarily mean that their account will be current.
This suggestion is based on family experience... they were having trouble understanding how they had a past due balance when they click "Pay my Balance Due" every month.
Thank you for your consideration!