Seeing how his YouTube tutorials helped his relatives and friends, Khan began posting more and more new ones in 2006. Students from the US and elsewhere started flocking to his videos.
In 2009, Khan left his job as a hedge fund analyst and founded the Khan Academy, an NGO dedicated to providing a quality education to anyone anywhere - for free.
"I teach the way that I wish I was taught," says Khan, 36, who grew up in New Orleans, in the US, and now lives with his wife and two children in California. He graduated from the Massachusetts Institute of Technology in mathematics and computer science and also has an MBA from Harvard University.
"The lectures are coming from me, an actual human being who is fascinated by the world around him," he adds.
The videos are short - they last from seven to 15 minutes. In voiceovers, he explains concepts and problem-solving techniques. Sometimes, he scribbles on a notepad, which appears on the screen, or uses diagrams as teaching aids. To date, Khan has made more than 3,100 videos for his website about a range of subjects from science to economics.
His website also hosts practice tools and rewards users with videogame-like awards for their performance. Users can track their progress in various subjects and measure themselves against others.
Khan's tutorial approach has won him many awards. It has also attracted Microsoft's Bill Gates, who invested US$1.5 million in his site in 2009. At a TED conference, Gates said he has used Khan's website to teach his own children.
In 2010, Google's "Change the World" fund provided Khan with US$2 million to support the making of more courses and translating them into other languages.
The internet is abuzz with students, young and old, who rave about Khan's videos. Some insist he is helping to revolutionise the US education system by building an online school for all.
Not that Khan isn't without his critics. Some educators have dismissed his videos as uncreative and said they are no different from the usual one-way lecturing format used in many traditional classrooms.
Others fault him for trying to replace flesh-and-blood teachers with impersonal videos.
Ada Wong Ying-kay, supervisor of HKICC Lee Shau Kee School of Creativity in Kowloon, agrees. "Education is about people and a face-to-face relationship between teacher and student remains crucial. A one-way tutorial approach fails to provide that," she says.
However, she appreciates the high quality of the videos. "He can turn a boring and complicated subject into something easy to understand," she says, adding "his work is inspiring and can benefit those who live in remote areas with no access to a classroom or teacher".
In an interview on CNN, Khan defended his approach and expressed his belief in the power of technology. "Perhaps we should rethink how we can [shape] the traditional academic model to how we can use technology. I think we're going to see some major changes in the next five or 10 years", he said.
To learn more, visit www.khanacademy.org