More than 1 million people have watched the online video in which Salman Khan--a charming MIT math whiz, Harvard Business School graduate, and former Boston hedge-fund analyst--explains how he began tutoring his cousins in math by posting short lessons for them on YouTube. Other people began watching the lessons and sending Khan adulatory notes. Khan quit the hedge fund, moved to Silicon Valley, and in 2009, with funding from a constellation of technology stars (Bill Gates's children were using the videos), launched the nonprofit Khan Academy. A year later, Mark Goines, a member of the Los Altos school board and a legendary Silicon Valley investor, introduced Khan to the district's superintendent. Los Altos already ranked among the best-performing districts in the state, but it had set itself a goal of improving individual achievement, and "capturing data at a granular level" on each student was difficult, Goines told the author. Los Altos agreed to pilot Khan Academy with two classes of 5th graders and two classes of 7th graders and provide Khan with feedback to refine the website and tools. By summer 2011, some 250 school districts, charter schools, and independent schools were asking to be part of the pilot and have Khan staff work with them to integrate the videos, data dashboard, and other tools into their curriculum. Los Altos is an affluent, tech-savvy community. The author wanted to see how Khan Academy could work in an inner-city classroom. So she visited Envision Academy, a downtown Oakland charter school, and Ruth Negash, a 4th-year teacher. In 2011, Negash taught two summer-school classes of 9th, 10th, and 11th graders who had failed Algebra I. One randomly assigned class used Khan Academy; the other was a traditional class. The results were promising enough that Negash now is using Khan in all of her 9th-grade algebra classes. Test results at both Los Altos and Envision suggest that Khan Academy is working. Both districts are quick to say that it is far too early to claim success: there were only 115 youngsters in the Los Altos pilot and 20 at Envision. "It's enough to say this is promising; it's not enough to say this is the future," Envision Schools chief academic officer Brian Greenberg said.