There is one highly cited (>1K citations in Google Scholar) study titled "Self-discipline outdoes IQ in predicting academic performance of adolescents", and quoting from its abstract:
Self-discipline measured in the fall accounted for more than twice as much variance as IQ in final grades, high school selection, school attendance, hours spent doing homework, hours spent watching television (inversely), and the time of day students began their homework. The effect of self-discipline on final grades held even when controlling for first-marking-period grades, achievement-test scores, and measured IQ. These findings suggest a major reason for students falling short of their intellectual potential: their failure to exercise self-discipline.
As a side-note, the author also gave a highly watched TED talk.
Given the usual replication issues in psychology, has this result been replicated, corroborated, criticized etc.?
And to put my doubt in a bit more perspective, in one large UK study (5-year prospective longitudinal, 70,000 of children) the correlation between IQ at age 11 and academic test score (GCSE) five years later was 0.81. And the same study setup repeated four years later on even larger sample of 175K obtained a similar correlation of 0.83. Alas the British studies didn't look at any measures of self-discipline, personality etc. The story in the US is not that different: ACT was found to correlate 0.77 with IQ on a large sample, while the correlation of SAT with IQ was 0.82 (0.87 when corrected for nonlinearity). I didn't dig into the paper to see at what age the IQ was tested in this case. On smaller samples, the correlation reported was less, for some reason that is unclear to me right now. However, one criticism of SAT/ACT which probably translates to the GCSE as well is that these tests themselves are a thin proxy for IQ testing (i.e. not enough knowledge is being tested in them.)