I've always (always) had the stance that nobody can really teach anyone anything. All learning comes from the individual doing the learning, as it can easily be shut out if they simply ignore it. Thus, if you're learning, you're trying at least a little. (exceptions being made for "teaching" under torture)
People (teachers) and tools can make it significantly easier / better / faster than learning on your own from other sources, but ultimately you are the one doing the learning. The ball's in your park. I go to school / class because I see the value in it. I also slack where there is little to no value, or when I've learned all the class has to offer. To do otherwise is ludicrous, as I could be spending my time learning other things, which is significantly more valuable to me. My grade is temporary. Learning is not. Which is more important? Also, if an employer doesn't see the value in intelligence / learning, and only looks at my grades, I do not want to work there. They clearly have backwards goals compared to mine.
Grades, as pertaining to this, are not a measure of learning. They're a measure of how well you can match the test's metric, typically rote memorization of facts. Learning is connecting facts, and being capable of extending them, and that's hard to test. It also rarely requires real memorization, as you instead build off X to get to Y; you don't need to know Y, just the method, and the method could be applied in a thousand places instead of just the one Y.