Salman Khan talks about how and why he created the remarkable Khan Academy, a carefully structured series of educational videos offering complete curricula in math and, now, other subjects. He shows the power of interactive exercises, and calls for teachers to consider flipping the traditional classroom script — give students video lectures to watch at home, and do “homework” in the classroom with the teacher available to...

It’s hard to believe YouTube is only five years old. How ever did we procrastinate without videos of babies break-dancing and chumps wiping out on treadmills? Then again, it’s also remarkable that the video-sharing site has lasted this long: five minutes is a more typical Internet life span. But YouTube — the world’s third most visited website after Google and Facebook — shows no signs of slowing down. The site marked...