If you just asked people "How smart are you" and correlated it with grades, you'd likely see a positive correlation. But if you give them Raven's Progressive Matrices, you'd see a much stronger correlation with grades.
That's not self-evident to me, if only because people's self-perception of smartness is likely to be (partially) driven precisely by their grades.
I agree that its very plausible that grades affect self perception. However, I have low confidence that it would be more predictive than IQ.
Same could be said for conscientiousness, but thus far it seems like the behavioral testing and the reports from grade-naive "homeroom" teachers seem to increase the correlation rather than decrease it compared to self-report alone.
The soon-to-be-resigning Dominic Cummings, advisor to the Education Secretary of the Coalition government, has released a 250-page manifesto describing the problems of the British educational establishment ("the blob" in Whitehall parlance) and offering solutions. I post this here because both his analysis and recommendations are likely to be interesting to LW, in particular an increased emphasis on STEM, broader knowledge of the limits of human reasoning and how they relate to managing complex systems, an appreciation for "agenty"-ness in organizational leadership, whole-brain emulation, intelligence enhancement, recursive self-improving AGI, analysis of human interactions on a firm evolutionary-psychological basis, and a rejection of fashionable pseudoscientific theories of psychology and society. Relevant extracts: