I've read in several places (not to spark any controversy) that Working Memory is probably the best indicator of academic success in elementary school. The particular study I'm thinking of measured working memory at the beginning of a child's schooling (around age five) and their subsequent academic progress at around age twelve.

I (think) the authors of the study were stating that working memory seemed to be the deciding factor independent of IQ score. (although working memory at least on the WISC is part of FSIQ- so a bit confused). Also, working memory was shown to be independent of parent's level of education or socio economic background.

I would be interested in seeing how working memory plays out as these children age through high school and college as academic subjects become more complex. I probably have a pretty excellent working memory (self-assessed) and was stymied by calculus and economics.