That's poor form from the school.

When I used to work as an integration aide, I was responsible for taking the children to the office to have their medication administered by the office staff.

Does he qualify for aide time? Could it be his/her job to remember?

Alternatively it's a PITA, but could you ring the office everyday at that time?
Hopefully it would only take a week of phone calls for them to get sick of you and suddenly remember!