ybbor
Will not change his avata
Good point, and there's another side to it too: diligent studying tends to make you smarter in the long run.
That's controversial for some reason. Actually I know the usual reason: many people want to divide "knowledge" from "intelligence". But that leaves you with a nonstandard and rather useless concept of "intelligence". So don't go there.
that's a great observation. I'll have to remember that.
(yes, yes, I'm very intelligent; I just don't know anything.

Some people seem to be insisting that GPA only indicates how hard you work, which to a large part is true. But I have never really sympathized with the argument that intelligence is unrelated to work ethic. There's too much variance in human intelligence to chalk it up to biology or environmental factors; some of it has to come with your ability to concentrate on a certain area and try to understand it. And like Ayatollah So said, "diligent studying tends to make you smarter in the long run."
A high GPA indicates someone who can understand difficult concepts (yes, I know, there are exceptions. Assume "introduction to underwater basket-weaving" is excluded), has an ability to concentrate and focus on tasks, someone who has good time management skills/can complete assignments efficiently, someone who challenges themselves, and someone who enjoys learning. If that's not intelligence I don't know what is.
"I'm really smart! I just can't be bothered to do any work." seems like an excuse from an idiot. These people don't challenge themselves, don't enjoy learning, and don't put in effort. A list of these people would stretch a mile wide. A list of people with high GPA's would be far shorter.
Spoiler full disclosure :
I have a high GPA. So my biases should be obvious, but it makes my arguments no less valid. (FWLIW I have high standardized test scores too)
oh, and I would assert that those talking about comparing different course loads (i.e. engineering to general studies; calc to pre-calc) are intentionally avoiding the question.