It will help your case out alot.
If they say they have it in writing, have them show it to you. Maybe ask why it is a problem now, after all this time.
but nicely!
(I give my sister liberty spikes now and again and she is in elementary/primary school...no one has said anything about it. it's a wide age range man)
I guess it depends on what they say about policy and stuff. Or if they threaten to keep you out of school until the situation is remedied. Maybe call the local news place? I'm sure the school would love the publicity... haha