new york city with bill weir. First the record stores, then crowds at the lie brabrary, and now you have to wonder if physical classrooms could become another casualty of the internet age. If kahn academy is any indication that the old schoolhouse will survive, but the way kids spend their time inside it could change forever. Why are millions logging on to get lessons from one man? Could your kids benefit? My co-anchor terry moran went to find out. Reporter: No matter how old you are, you can probably still remember what the bell sounded like in your school. You can still remember pushing your way through the hallways to your next class, or the minute hand on the clock in your math class that you score ran slower than every other clock in the building. This is now. Eight meters. And the same thing along the side. Reporter: Welcome to the kahn academy. Online learning on steroids. A one-world schoolhouse that is skyrocketing to popularity, sparking controversy and fundamentally challenging the very notion of education in the 21st century. What we're tackling right now is the learning side. How can we democratize is information, the knowledge, so that anyone can get to whatever level they want to. Reporter: Sal kahn founded the kahn academy kind of by accident. More on that in a minute. First the sheer scale of this thing. Seven million students around the world are attending the kahn academy online every month, and that number is growing by 400% per year. The thousands of lessons, everything from algebra to medieval history to the fiscal cliff, they've been viewed more than 200 million times. And all for free. Are you out to dismantle our educational system? I'm not an education radical. A lot of what I'm doing and we're doing is really bringing back very, very old ideas that have been proven, but somehow got lost in the fray. Reporter: Sal kahn is an unlikely education reformer. He's a former hedge fund analyst, m.I.T. Undergrad, harvard mba, who just stumbled upon his revolution when he tried to help a young cousin with her algebra homework back in 2004. I started tutoring her remotely. I was in boston, she was in new orleans. After that, I started tutoring other family members and eventually put the stuff on youtube. Reporter: In a few weeks, kahn noticed that the stuff he was making for his relatives was going viral, requests from strangers for more, more, more. Visually, they aren't the kind of videos you'd expect to go viral. They're more of a virtual blackboard. But they work. And education reformers all over the world have noticed, including some heavy hitters. There's a website that I've just been using with my kids recently called kahn academy. Just one guy doing some unbelievable 15-minute tutorials. Reporter: Bill gates did more than look at the kahn academy videos. He helped to bankroll the project. So in 2009, kahn finally quit his day job and partnered with the gates foundation and google to form the kahn academy. Students watch the videos and then work on a problem set based on the lesson on the website. If you pass, you move on to the next lesson. If it looks like you don't understand the concept, the site takes you back through what you are missing. The idea of students being grouped in age-based cohorts and then going at a set pace, this is the school we all grew up in. This is actually not the way students were educated for most of history. Reporter: Instead, kahn and his allies seek classrooms tluming with creative activity, spurred by the fact that kids will have already engaged the subject matter through the online lessons. What is your ideal classroom look like? It won't be a bunch of chairs all positioned looking at someone in the front of the classroom. It will be a much more collaborative pace. It's not one size fits all anymore. The teacher will be doing focused interventions with them, they'll be inspiring them, they won't be lecturing at them. Reporter: About 25 to 30 schools have started simp ed implementing the kahn academy, exploring how it might change teaching and learning. There are plenty of critics but one big group of supporters. The single biggest thing that happened, and it wasn't obvious to us at first, the teachers and the principal told us, is that the students started to take ownership of their learning. They started to not say I'm passive, tell me what to do next. They started to say these are my goals, I'm going to seek out the information, teacher, you are my coach, you're my mentor, help me do it. Reporter: They're already online, maybe at least in some ways, that's where their classrooms can be, too. And kahn's book "the one world schoolhouse" is in stores now. When we come back, the u.S.