In this day and age I would of deleted the photo and left it at that but maybe I look at it differently with working in a school part time.

Also if the parent was sitting behind you perhaps a a discreet chat with her (if she seemed decent enough which most people are) and say this is the shot I took. Would you be happy if I deleted it?

It's like I wouldn't dream of taking a photo of a scholars service and uploading it to Flickr. What happens if you can clearly make a kids face out on that photo, that said child is in care and the parents don't know where the child is living. They then see there on a bus to St Roberts School and boom! Perhaps I over think like I said...