Better beginning preparation can bring up a whole national average to about the "gifted" level in the United States, in several countries that were formerly poor and backward,

http://nces.ed.gov/pubs2009/2009001.pdf

and several aspects of primary curricula in the United States are KNOWN to be suboptimal,

http://www.ams.org/notices/200502/fea-kenschaft.pdf

so there is surely still a lot of room for improvement in the United States.

Genius is primarily a learned skill. Yes, some people have more aptitude than others, but the vast majority, if they apply themselves, will do just fine. It's far more a question of a support structure to instill discipline than it is of innate skill. Those who truly cannot learn and maintain discipline are rare.

Just to share a quote that motivated me in university (and turned my grades around dramatically)

"Nothing in the world can take the place of persistence. Talent will not; nothing is more common than unsuccessful men with talent. Genius will not; unrewarded genius is almost a proverb. Education will not; the world is full of educated failures. Persistence and determination alone are omnipotent"