Unless you are forcing them to use the home access, it is their choice to access it from home. For example, If a school is providing a bus service for free which will collect staff, but a member of staff chooses to drive to school then they can't claim petrol.

You have provided yet another means of access to a school system, use of it through that access method is up to them. We had something similar, teachers thinking they could claim consumable costs for their ink at home, because we have restrictions here. The school provides printers, they choose not to use them. They can come to us if they have a big job to be printed.