The classroom at Sree Karpagavalli Vidyalaya Middle School in the Indian city of Chennai is full of teenagers who have gathered for their maths class. But there is a pretty major problem: they have no teacher. He left several months ago.
The school now has half the staff it had 10 years ago; the number of pupils has dropped by two-thirds in the same period, largely because more and more parents are choosing to send their children to English-language private schools.
But these pupils are still here and they are busy working. They are hunched over computers, watching video lessons.
As far as most Indians are concerned, Salman Khan is one of the biggest stars in the history of Bollywood cinema. But that's not the Salman Khan these children look up to. The Khan they know is a 36-year-old former hedge fund analyst based in the US who prefers to be known as Sal. For them, and for hundreds of thousands of other people of all ages across the globe, he is their teacher.
Eight years ago, Khan first dabbled in online tutoring to help his cousin, who was struggling with algebra. Three years ago, he quit his lucrative job to pursue his new-found passion for online learning full-time, setting up a makeshift office inside a walk-in wardrobe.
The following year, he received a text that would change his life. It was from a fan who was attending an ideas festival in Colorado. It simply said: "Bill Gates on stage, talking about you."
Today, Khan's website - Khan Academy - offers more than 3,600 video lessons. He has filmed the majority of them himself. But this is no two- bit operation. The site attracts 6.5 million unique users a month and its videos have been viewed more than 200 million times. "That's a big number," Khan admits, with some understatement.
And his fans are not just traditional educationalists. Khan has appeared on the cover of American business bible Forbes. This year, he was named one of Time magazine's 100 most influential people in the world.
Khan's citation for the prestigious listing was written by his most famous benefactor: Gates. But the Microsoft founder's interest isn't just philanthropic. "I've used Khan Academy with my kids," he wrote, "and I'm amazed at the breadth of Sal's subject expertise and his ability to make complicated topics understandable. He started by posting a math lesson but his impact on education might truly be incalculable."
Gates is just one of the billionaires queuing up to pump millions of dollars into the project. For Khan, the work has only just started. One day, he envisages 100 million people across the world using his website on a regular basis.
Rather than seeing online learning as a replacement for the physical school building, Khan has some radical ideas about how education should look in the future. As the public face of the "flipped learning" movement, he believes that basic learning should be done by video before a pupil arrives in class. The lesson can then be used to explore the subject matter in depth and iron out any problems on an individual or small group basis.
The implications for the teaching profession could be profound. Khan envisages pupils being taught in "super-classes" of 100 with three or four teachers, and has called for the abolition of separate subjects and even the summer holiday break. TES was invited to California to meet the man Gates has described as a "true education pioneer".
Khan may share a zip code with global giants LinkedIn and Google (another major benefactor) in the heart of California's Silicon Valley but the office where most of his work takes place is surprisingly low-key, sandwiched between a Chinese furniture store and a fashion boutique on the leafy main street in the town of Mountain View.
Khan, wearing chinos and a T-shirt, strolls down the stairs to let me in. It is easy to see how his laid-back style - his speech is littered with "kinda" and "like" - is popular with learners.
Most of the Khan Academy videos follow a set pattern. The viewer hears Khan's voice but never sees his face. Using a visible cursor, he writes or draws on a blank, black screen, like a traditional blackboard. Crucially, what the viewer sees is exactly the same view that Khan sees when he's making the video.
The videos are never scripted, always improvised. Khan believes his relaxed manner puts learners at ease. "People seem to think, `This is, like, one dude. I have sat through 30 of his videos, I feel like I know him.'"
This personal connection, the feeling that the teacher is on the learner's side, is key. "In many classrooms," he explains, "the teacher is the policeman, the assessor, the person who's going to ascertain whether you're smart or not smart, not necessarily the person who's on your side."
Khan recalls one of his own teachers, Mr Hernandez. Khan knew him through the school maths club and "absolutely loved" the algebra teacher; in contrast, his friends in Mr Hernandez's regular class dismissed him as a "hard" disciplinarian. "That was really just (about) how we interfaced with the same guy," Khan says. "He's genuinely a good guy, he genuinely cares about how people learn, but at the end of the day he's stuck in this Prussian model."
In his book The One World School House: Education Reimagined, Khan uses the term "Prussian model" to denote the traditional school orthodoxy, with set timetables, subjects, behavioural codes and teaching styles. Khan believes that this top-down approach has tended to, whether by accident or design, "stifle deeper enquiry and independent thought".
Khan's cousin Nadia is a case in point. In 2004, while he was living in Boston, he offered to tutor the 12-year-old, who lived in New Orleans, over the Yahoo! Messenger chat program, after hearing that she was struggling with her algebra. After initial difficulties on both sides, Khan came to realise that it was Nadia's failure to grasp a relatively simple concept - unit conversion - that was holding her back. He decided to concentrate on this and gave her plenty of encouragement.
Two months in, he noticed that "something clicked in Nadia's head". She started to understand. "And not only did she get it," Khan says, "but it started to really accelerate, she started to really engage. When I saw that, I thought, `This is something.' It made me think there might be other Nadias in the world. As soon as she had this ownership mentality, it became almost trivial (sic), easy to expose her to new things."
Khan then started to help Nadia's younger brothers and developed simple software to track their progress. "I saw them accelerate to a point that we'd always assumed was (a sign of) genius - if a kid was 10 and learning (such) advanced algebra or trigonometry," he says. "I thought my cousins were probably smart and all that, but it seemed (that this was) something we could do consistently, as long as the student wanted to learn. I was excited."
Khan decided to start filming lessons and posting them on YouTube. This was intended to be a means to an end; after all, he was firmly of the view that the video-sharing website was "for dogs on skateboards, not for serious mathematics".
But he quickly realised that his "stupid" videos were exactly what was capturing people's imagination. He unwittingly found himself at the centre of the flipped learning movement.
From sage to guide
In this pedagogical model, the role of the teacher shifts from being the "sage on the stage" to the "guide on the side". The basics are taught before the pupil even sets foot in the classroom via online videos, which take a traditional lecture-style format to convey the core content. Learners can watch at their own pace, and pause and rewind as they wish.
This fundamentally changes the nature of the classroom lesson, which becomes about the teacher giving focused attention to individual pupils. The teacher can use software to track each learner's work, devoting their time accordingly.
To the average teacher in an inner-city secondary, it may be difficult to imagine that a challenging Year 9 pupil would have the self-discipline to direct their own learning. Khan, though, is convinced that this natural curiosity exists in everyone.
"Almost every four- or five-year-old takes ownership of their learning," he explains. "You have to stop them. You have to say, `Stop bugging me! Here, let me get my phone back, stop exploring my phone. This is Dada's book, stop.'" Khan laughs. As a father of two, he has learned this the hard way.
But these innate qualities are still prevalent in teenagers, he believes. "This is the thing that the video game creators tap into to make them so addictive: humans' natural desire to accomplish things, to achieve and explore. The same kid is flunking his math class, but spending 20 hours doing research on the web finding out how to beat a game."
This focus on skills and creativity does not appear to sit comfortably with the educational ideology underpinning education secretary Michael Gove's current reforms in the UK. Last November, Gove argued the importance of "memorising scales, or times tables, or verse, so that we can play, recall or recite automatically".
So what does Khan think of Gove? He shrugs his shoulders. "I don't know his exact details," he admits. "As long as the way it's happening is not ultra rigid, I don't think it's the end of the world if a kid's memorising the kings and queens of England. But if that's all they're doing, and if they don't then have the opportunity to take that and write a story or do something else interesting with it, then it's beside the point."
Ironically, Khan's critics have denounced his videos for perpetuating exactly this style of rote learning. Former maths teacher Karim Kai Ani, who works for the Mathalicious website, has been one of Khan's most vocal critics.
While the flipped classroom is supposed to mark the end of regurgitated memorisation and repetition, Ani argues that Khan actually relies on that approach himself. "It's exactly that," Ani says. "Objectively, Khan Academy isn't that great. The teaching isn't very good. The only difference is that it's on YouTube. We're trying to solve the problem with something that looks exactly like the problem.
"I admire what Khan's done. He's done thousands of videos; it's a great resource for a student who needs some extra practice. But that's not how people are seeing it, because Bill Gates has come along and said this is the world's best teacher. He's essentially reciting a textbook on a video, and now he's one of the 100 most influential people in the world. The whole thing is absurd."
And with the high-profile support that Khan's videos attract, Ani fears that officials might see them as a cheap replacement for teachers. "It reminds me of tackling the obesity epidemic. We need to exercise and eat better but instead people go on the Atkins diet. This is the educational equivalent of the Atkins diet."
Khan is all too familiar with Ani's criticisms. He smiles. "I know that guy." But it's clear that Ani has got under his skin. "Essentially, his narrative - which isn't necessarily the best way to endear someone (to you) - is, `You seem like a great guy but you're a complete idiot. You need my help.'"
He sits back in his chair. "People read about something and they form an initial kind of knee-jerk opinion. (They think) it's this guy who's not an educator; it's being funded by people in the computer industry. They must think it's about creating videos to replace teachers. I'm, like, no. We fully appreciate what a great teacher can do.
"We take feedback very seriously but it's important that we don't lose what has (given us) the traction that we have so far. On the specific critiques, the one I would agree with is that we're not a silver bullet. Where I disagree is that I never claimed that we were a silver bullet."
But the hyperbolical praise lavished on Khan Academy - "Can Salman Khan save education?" asked Time this summer - means there is no shortage of critics queuing up to have a pop. In June, two maths lecturers from Grand Valley State University in Michigan posted a parody video on YouTube in which they pick holes in one of Khan's videos on negative numbers. It has been viewed more than 42,000 times.
As the clip starts, one of the men quips: "This is going to be amazing. It's like the best teaching millions of dollars can buy." As Khan's video starts to roll, the mockery from the two silhouettes in the foreground continues. "So we should start with the thing that's most confusing and end with the thing they already know?" the other professor asks. After picking up on several apparent errors by Khan, one of the men bluntly concludes: "If Bill Gates thinks he's the best teacher in America, that explains a lot about Windows."
Khan's original lesson has now been taken down. "There was an old video where I bumbled around with something," he admits, "and I'm like, yeah, that's not cool. I should redo that video."
Although much of Khan's work is online, he tells TES that he would love to open a physical Khan Academy school one day. Pupils, he says, would spend between one and two hours on "core" learning, with the rest of the day spent exploring concepts in more detail and directing self-led projects.
Khan believes that a couple of hours a day is more than enough for "proper" learning, pointing to pre-exam cramming as evidence. "We've all done it," he says, becoming more animated. "We've learned an entire term in, like, two nights. It shows you what's possible. On top of that, think about how much of a child's school day is actively learning. It's not even two hours.
"So, yes, two hours a day is 10 hours a week. In a semester, that's 90 hours of learning. Over a year, that's 180 hours of learning." He looks expectant, as if waiting for approval.
`A monumental waste'
But this is a man who has the courage of his convictions. He is certainly not afraid of tackling the orthodoxies of the educational establishment, including one of the most sacred cows for teachers and children alike: the summer holiday. This is a "monumental waste of time and money", Khan writes in his book. "Around the world, tens or hundreds of billions of dollars (worth of) education infrastructure - school buildings, labs, gymnasiums - sits vacant or, at the very least, seriously underutilised. Teachers don't teach (during the summer months)."
Most significantly, Khan argues that pupils almost immediately start "unlearning" as their newly created neural pathways begin to break down. "Give a kid 10 weeks off school, and it's neither metaphor nor exaggeration to say that some of what he used to know about algebra vanishes from his brain and gets reabsorbed into his bloodstream," he writes.
As in the world of work, pupils should be able to take their holiday allocation throughout the year, Khan says. "People say, `Summer vacations were the only times in my childhood where I got to be a child, where I got to explore and be curious.' Why isn't that school? Why isn't school that place that fosters your curiosity?"
He calls for an end to topics being split into separate, arbitrary subjects. These, he claims, stifle intellectual exploration. In contrast to the rigidity of the Prussian model of schooling, he nods approvingly at the private tutors for the wealthy in centuries gone by. "Chemistry is really just a different layer of abstraction of physics, and I don't think they would have separated them. Now, we're like, `Oh, wow, how is that person an artist and a physicist and a mathematician?' That was the norm for an educated person 300 years ago. You look at Thomas Jefferson or Benjamin Franklin. How come we don't see more (people like that) now?"
Khan's book also advocates a potentially even more radical demolition of traditional school structures: the end of grouping pupils by age. "That isn't how families work," he writes. "It isn't what the world looks like; and it runs counter to the way that kids have learned and socialised for most of human history. Both younger and older kids benefit when different ages mix. The younger ones look up to and emulate the older ones. Everyone seems to act more mature."
In Khan's vision of super-classes, the three or four teachers can work in tandem or separately; similarly, the pupils - all different ages - can work in small groups, large groups or individually. Gone would be the days of tidy ranks of desks all facing the front of the class. The pupils, Khan writes, "would seldom if ever all be doing the same thing at the same time". While some would be quietly working at their computers, other parts of the room would be "bustling with collaborative chatter".
So does this mean that schools need more computers and fewer teachers, I ask. Khan flinches. "I'm not advocating that. I think the more, the better. Let's not use this as a cost-cutting device; let's use this to improve outcomes. You can never say you're spending too much on education. But you can say that what you're spending, you are spending badly."
The sheer number of people using Khan's videos means he arguably faces more scrutiny than any other teacher in the world. So what does it feel like to have hundreds of thousands of learners across the world hanging on your every word? Khan looks uncomfortable. "I try not to think about it too much. I think about it, obviously, but I prepare as much as I can prepare without it paralysing me. But sometimes I do feel that."
For Khan, though, the hard work has only just begun. "There are a million things in my head that I know need to be improved on at Khan Academy," he says. "We're at stage 0.1. I can't wait until we're at stage 100. It's going to be so much better."
Khan Academy employs 36 people. Its website (www.khanacademy.org) has more than 3,600 videos on a range of subjects, from maths and chemistry to finance and history. The site also offers an "exercise" system that, based on pupils' skill level and performance, generates questions or problems for them to solve.
A data "dashboard" allows teachers to monitor how pupils are doing, as well as generating class reports. Pupils can measure their own progress by earning points and winning badges, and view their overall performance on a knowledge map.
Sal Khan CV
1990-94: Grace King High School, Metairie, Louisiana, US
1994-98: Massachusetts Institute of Technology. Gained two BSc degrees (electrical engineering and computer science; maths) and a master's in electrical engineering and computer science
1998-99: Senior product manager, Oracle Corporation
1999-2001: Technology director, MeVC Venture Capital
2001-03: Harvard Business School. Gained a master's degree in business administration
2003-08: Senior analyst, Wohl Capital Management
2008-09: Senior analyst, Connective Capital Management
2006-present: Founder, Khan Academy
Thousands of Khan Academy videos are available to be viewed or downloaded from the TES Resources website. www.tes.co.ukkhanacademy.
Photo credit: Alamy