The site covers a staggering array of topics-from basic arithmetic and algebra to the electoral college and the French Revolution. It's those latter statistics that motivate Khan. About a fifth of American 15-year-olds do not have basic competence in science 23% can't use math in daily life. is the only developed country to have high proportions of both top and bottom performers. And, as in so many other areas of American life, those averages obscure a deeper divide: The U.S. ranks 25th out of the 34 OECD countries in mathematics, 17th in science and 14th in reading.

America spends the most-about $1.3 trillion a year-yet the U.S. How immense? According to a report from the President's Council of Economic Advisers, global spending on education is $3.9 trillion, or 5.6% of planetary GDP. And that creates immense opportunities for both for-profit entrepreneurs and nonprofit agitators like Khan. After decades of yammering about 'reform,' with more and more money spent on declining results, technology is finally poised to disrupt how people learn. It's a fair question, with an increasingly sure answer: The next half-century of education innovation is being shaped right now. The company's 37 employees, mostly software developers with stints at places like Google and Facebook, are the types who know when to laugh. It involves LeBron James (a Khan Academy fan), three-point shots and sophisticated algorithms called Monte Carlo simulations. Pivoting, Salman Khan, the 36-year-old founder, cracks a sports joke appropriate for someone who holds multiple degrees from MIT and Harvard.

At the weekly organization-wide meeting, discussion about translating their offerings into dozens of languages is sandwiched between a video of staffers doing weird dances with their hands and plans for upcoming camping and ski trips. Despite the cramped, dowdy circumstances, youthful optimism at the Khan Academy abounds.

The headquarters of what has rapidly become the largest school in the world, at 10 million students strong, is stuffed into a few large communal rooms in a decaying 1960s office building hard by the commuter rail tracks in Mountain View, Calif.

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