Prevents? No. I didn't say that. But being poor usually means you don't have access to the same levels of education. Read the comments in this thread. http://news.ycombinator.com/item?id=520836
No -- you didn't say anything about education level, which is tangential to GPA. What you said is "judging on the basis of GPA alone is class discrimination. Poor people don't stand a fighting chance." In other words, if you're poor, you don't stand a chance of (i.e. are prevented from) being able to achieve a high GPA. My experience says differently.
I've read one of Gladwell's other books, and I think he makes the same mistake you are making. A correlation does not necessarily imply "discrimination" or that the odds can't be overcome. For instance, women have higher GPAs than men, on average. That doesn't mean that using GPA as an indicator of performance discriminates against males. It might mean that males might need to work harder or do something a bit differently in order to get the same GPA.
In the end, my admittedly subjective take is that the biggest factor is individual motivation. We all have our setbacks and obstacles to overcome, but that's just the craps of life. I can verify, however, that it is indeed possible to go from moving out of your house at 16 with no money to graduating Phi Beta Kappa from Stanford (not me, but someone very close to me). Difficult, yes... but it shows that there is almost always a "fighting chance."
Alright. You got me. I shouldn't have made such a strong statement, but I think it's safe to say that you would atleast be put at a pretty big disadvantage. But you're right in that wherever there is a will, there is a way.
