If he had flunked out, wouldn’t they have snapped his wand, like they did to Hagrid?
More to the point – if he flunked out, why on Earth would they invite him back to teach?
Who knows… but he obviously didn’t know magic outside of memory charms. There is the possibility that he never went for formal education, but was home schooled (or the equivalent).
They may have invited him back because of his fame.
I mean is there any requirement that you have to go formal school to keep your wand? Is there like a GED for wizards?
Maybe Lockhorn was such a whiz at memory charms that his teachers never realized that he was an idiot, either. (He charmed them all.)
I never thought I’d join in a Harry Potter thread. I believe the wand-snapping is what they do at Hogwarts. Other wizarding schools may do different things.
Dissing Dumbledore?! That’ll cost you 500 points!
Dumbledore is also 150 years old, probably due to the Philosopher’s Stone. I’m guessing we’ll get more of his back story in Book VII, and perhaps that of his brother who’s been referenced several times and is the barkeeper in Hogsmead, but has never been developed. I think it’d be cool to learn that Dumbledore and his brother are Muggle born (though I don’t think they are as the Malfoys would surely have made a crack about it by now).
in goblet of fire, dumbledore smashes down the door and stupifies crouch. crouch was attempting to do in harry.
that was when harry saw why dumbledore is so feared. it was very much as ethilrist said. he doesn’t walk around using his full power all the time. it is there when he needs it. he makes a seamless transition and kabam you don’t know what hit you.
Yes, but that’s in Earthsea. 
Actually, I think that’s right. Lockhart is not a totally bad magician; he just didn’t do any of the things he said he did and has spent so much time collecting other wizards’ storie and writing books, he has lost all his magic skills except memory charms. He’s probably the best memory charmer out there, so good he even fooled Dumbledore.
Actually, that’s just because wizards live longer than Muggles. Probably due to the availability of all sorts of curative magic.
And Gilderoy Lockhary could’ve gone to school without learning anything. Do you think, for example, that Crabbe or Goyle can do much magic? From their constant characterization as barely-literate oafs, I’m betting JKR has them getting “Ts” on some of their OWLs. 
And think about how many Muggle HS graduates can’t read, do long division, or name the three branches of government. I’m sure students slip through the cracks at Hogwarts.
It’s suggested that heads of Houses favor their own students (see Severus Snape). Maybe Lockhart was a favorite of Flitwick’s, hence the charms he knows? That suggests Ravenclaw, which is so wrong…
I thought they only snapped your wand for being expelled, not for failing.
Yes, I agree-Speaker for the Dead is correct about the epulsion. And Hagrid was found guilty of encouraging magical creatures (or at least possessing known to be dangerous beasts)–I dunno if Hagrid would have failed at Hogwarts–he wasn’t given the opportunity to complete his education. He certainly does a good job at fobbing off Umbridge et al in OotP–and he keeps that pink umbrella…
He may be stereotyped as a working class rural loutish type–but Hagrid’s skills and abilities are recognized by Dumbledore at least.
I liked that bit in GOF when Crouch was attacking Harry and AB comes in–to me it reveals the hidden strengths of AB. Very Gandalfion (and that’s a good thing) --also quite Merlin-ish.
I think the real reason why Voldemort fears Dumbledore is not because of Dumbledore’s power, per se. It’s because Dumbledore does not fear Voldemort. Like so many Dark Lords, Voldemort’s power is built chiefly on fear. When someone doesn’t fear Voldemort, he has that much less power over that person. And what he can’t control, he fears.
No, I think Rowling said wizards live longer than Muggles.
Dumbledore’s basically nice guy until he’s pissed schtick makes me think of my dad. My dad’s a really nice, mellow guy-but when he’s pissed off, he’s SCARY. And not in a harmful, or abusive way, just someone you don’t want to fuck with.
Lockhart could possibly have done poorly on his O.W.L.s, with a few failing grades, and a couple of Acceptables. Presumably, this could leave him facing a sixth year with few or zero opportunities to take N.E.W.T.- level coursework (maybe Charms). There’s a possibiliity that he didn’t even achieve a passing grade in a single N.E.W.T., left Hogwarts Summa sans Laude (be gentle; I just made that term up), and somewhat accidentally stumbled upon his ultimate callling - ersatz Dark Arts fighter/memoirist. His real-world experience could conceivably have qualified him for the jinxed post.
One supposes that Stan Shunpike and Ernie Prang landed in their own careers through similar means (albeit without the massive fraud).