A school for wizards, how original, was many people's original reaction to J.K. Rowling's Harry Potter books. And over there in a corner was Ursula K. Le Guin, waving her hand and saying, "Excuse me, but I did that back in 1968." Nothing wrong with admiring Rowling's stories or what she did with the concept of such a school, but you can't credit her with being the first to originate it.
What nobody seems to have asked is whether there's any actual relationship between Hogwarts and Roke in Rowling's creative imagination. Nor has anyone to my knowledge brought attention to a relevant datum on this subject that came out a couple years go. In a New Yorker profile of Rowling on the occasion of the publication of The Casual Vacancy, writer Ian Parker interviewed her secondary school English teacher, a man named Steve Eddy, who says that his syllabus for class reading included A Wizard of Earthsea (along with Garner's The Weirdstone of Brisingamen, a book which I'd say resembles Harry Potter in tone a lot more than anything in Earthsea does). [New Yorker, Oct. 1, 2012, p. 56]
This was when Rowling was aged 11, so it would have been 1976-77.
I loathe the sort of criticism which predetermines that every author's good ideas are borrowed from some other author. And even if Rowling remembered Le Guin's Roke, it doesn't necessarily follow that the idea for Hogwarts came from there. They're quite different places, and the derivation of Hogwarts from a hearty British schoolboy story with the addition of wizards seems far more likely. Nevertheless, just as a datum, let it be recorded: Rowling as a child read, and therefore had access to, Le Guin's A Wizard of Earthsea.