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. The Khan Academy, which features 3,400 short instructional videos along with interactive quizzes and tools for teachers to chart student progress, is a nonprofit, boasting a mission of "a free world-class education for anyone anywhere." There will be no IPO; funding comes from philanthropists, not venture capitalists. The next half-century of education innovation is being shaped right now. Global spending on education is $3.9 trillion, or 5.6% of planetary GDP. America spends the most-about $1.3 trillion a year-yet the U.S. ranks 25th out of the 34 OECD countries in mathematics, 17th in science and 14th in reading. It's those latter statistics that motivate Khan. The site covers a staggering array of topics-from basic arithmetic and algebra to the electoral college and the French Revolution. The videos are quirky affairs where you never see the instructor (usually Salman Khan himself, who personally has created nearly 3,000 of them). Instead, students are confronted with a blank digital blackboard, which, over the course of a ten-minute lesson narrated in Khan's soothing baritone, is gradually filled up with neon-colored scrawls illustrating key concepts. Over the past two years Khan Academy videos have been viewed more than 200 million times. The site is used by 6 million unique students each month.