There has been some nonsense spouted here.
Are there really parents who are too busy/disinterested/important to attend hospital if their child requires assessment/treatment? As for "you broke them, you fix them", really? As a parent you want no input in the recovery of your child?
I have sat holding the hand of a very scared 12 year-old girl, strapped to a backboard, getting an x-ray of her spine. I took the responsibility of asking her if she thought there may be a chance that she was pregnant. Not a question that most 12 y-o girls are comfortable with, despite what you read in the media, and to have been asked it by a total stranger would have added further distress. That was a case where Mum was a long way away and totally unable to attend.
If an accident happens in school, my working assumption is that the parent wants to be involved. If the child is severely injured, 999 all the way, but a less severe, stable injury does not warrant an ambulance, and in my experience, without exception, parents are happy to collect their child from the school. "Meet us at the Hospital." will induce panic in most Mums and Dads. Picking the child up from the school also freaks the kid out less too. Always a child would be made comfortable and fully supervised whilst waiting for the family.
There is also an opportunity for a conversation, maybe brief, but important nevertheless, about the circumstances of the incident, and any steps the school is taking, as well as the early ability to address any concerns or expectations from the parent.