How does the Hogwarts Headmaster know whom to invite to school?
In Harry Potter universe, not everyone can do magic. Only magic users can do that. But, how to identify a newly borned child that he/she is magic user or not?
In Star Wars universe, we've midi-chlorians existence using which we can identify someone as force user. I was looking for similar things without any luck.
How does Wizard and Witchcraft universities send invitation letters to 11 year kids?