I read somewhere (sorry, can't remember the source - but it had to do with research from the neurologist Hughlings Jackson) that very early reading (not necessarily very early proficiency with numbers) is highly correlated with giftedness in math. The idea behind this is that early reading requires working with a closed-symbol system, which is also used in higher-level math. In fact, according to this theory, children who are very early readers are not necessarily exceptional in literacy or writing (use open-symbol systems). That was my take home message from that article anyway. I'll try to hunt down the source...
