I'm not entirely convinced it's a very good proxy (at least for the hard sciences). Certainly in my physics classes, raw-intellect trumped conscientiousness; using tidiness as a proxy for conscientiousness and "holds an advanced degree from a distinguished university" as a proxy for GPA, a walk-through of the professors offices in that same department would also dispute that.
I think GPA is closer to a proxy for (A + g) * (B + conscientiousness) with values A and B varying from school to school and department to department (as well as the threshold for "perfect" varying). I had 3 roommates with higher conscientiousness than me flunk out, so YMMV.
[edit]
While we are talking personality traits, I think a high GPA is probably also a proxy for neuroticism; certainly many of the straight-A students exhibited these traits (as does the child of mine who gets the best grades). FWIW I score low in both conscientiousness and neuroticism on a Big Five test.
[edit] changed from "not convinced this is true" to "not convinced it's a very good proxy"
I think GPA is closer to a proxy for (A + g) * (B + conscientiousness) with values A and B varying from school to school and department to department (as well as the threshold for "perfect" varying). I had 3 roommates with higher conscientiousness than me flunk out, so YMMV.
[edit]
While we are talking personality traits, I think a high GPA is probably also a proxy for neuroticism; certainly many of the straight-A students exhibited these traits (as does the child of mine who gets the best grades). FWIW I score low in both conscientiousness and neuroticism on a Big Five test.
[edit] changed from "not convinced this is true" to "not convinced it's a very good proxy"