It seems that today anyone that wants to talk about wizards references Harry Potter. Even if you haven't read it or don't like it, it seems that HP is a standard. Anytime you write something about wizards in training, or especially wizard schools, someone's going to compare you to HP. I know Rowling didn't do anything innovative in creating her world, but she seems to be the standard.

It led me to think, what was there before HP? Was it just JRR Tolkien, or were there others where everyone said this is what you have to measure up to. And, was there anything where if you referenced someone to it, they'd understand. A lot of my comparisons come from HP because I know people are familiar with it.

I also think that The Dark is Rising sequence had a good deal of magic in it, as well as The Wrinkle in Time series. They just seem to have faded away since Harry Potter made it big.

Of course, we can't forget the Chronicles of Narnia, although in some cases, Lewis actually seems to separate magic into two realms. There is the ritual magic that is shown in the Magician's Nephew and alluded to in Prince Caspian. Both of these examples show that Lewis didn't think much of the incantational magic. However, there is the "spiritually creative" magic that is invested in Aslan and the Emperor Over the Sea that seems to be some higher form of magic.

As for wizards in general, you wind past Tolkien through E. R. Eddison and Lord Dunsany and William Morris and then take a deep dive back to Merlin and his role in the life of King Arthur. There are any number of sidebar splits (note the "evil scientist" in SF from Frankenstein on down), but that's more or less the main line. Unless I missed a connection somewhere, or misremembered details.

On wizard's schools, well, Rowling's schools resemble the English public-school stories, just with fantastic elements added. Hogwart's is just a supernatural version of Eton or Harrow or any of a few others.

As for wizarding schools, i don't know that there was any book that was famous for it. i seem to remember a British book called Bed-Knob and Broomstick by Mary Norton, but the details are too fuzzy. I think it had to do with a school, but i doubt that book was well known enough to be called a standard.

Edit: I'll add that even Tolkien wasn't that well known outside of the Fantasy genre, at least until after the movies. Many may have heard of him, but not as many were familiar with the story. Not, certainly, like HP, where people who'd never read a lick of fantasy read all the HP books (and some who insist they don't belong in the fantasy genre--go figure).

Before HP there were stories of kids at boarding schools, of kids solving whodunnits despite the grownups, and of kids and witches and wizards. But HP brought all three genres together, made it fun and didn't bother with YA political correctness.

As to fantasy, there were tons beside Tolkein (although Tolkein was, and is, the end all beat all) I think back to Junior High, everyone was reading the Dragonlance books. You still won't find a more fleshed out world than Krynn, (considering there is around a hundred novels about it). Then there was Robert Jordan, they were calling the Wheel of Time the next LOTR. Of course there was A Wrinkle In Time, that was a quite important book for me. Lloyd Alexander's Pyrdain. (I know these have been mentioned but I want to add my votes for them.) Narnia.

Among the more obscure, there was one called the Gammage Cup that was fantastic.

There was plenty before HP and personally I never think of them unless someone brings them up. They are hardly the "standard" for fantasy in my mind.

Edit: I had to agree that Rowling's wizard school seemed very similar to Le Guin's in concept but maybe any wizard school would. Le Guin invented the idea as far as I know (maybe not but I can't think of anyone who did it before she did).