Professor Binns always calls the students with different last names - for example, for Harry, he says:
"Off you go, Perkins."
Harry Potter and the Order of the Phoenix
or to Hermione:
He stuttered to a halt. Hermione’s hand was waving in the air again.
‘Miss Grant?’
‘Please, sir, don’t legends always have a basis in fact?’
Harry Potter and the Chamber of Secrets
or to Parvati:
‘But, Professor,’ piped up Parvati Patil, ‘you’d probably have to use Dark Magic to open it –’
‘Just because a wizard doesn’t use Dark Magic, doesn’t mean he can’t, Miss Pennyfeather,’ snapped Professor Binns. ‘I repeat, if the likes of Dumbledore –’
Harry Potter and the Chamber of Secrets
Is there a reason behind this?