How many students does the average teacher teach in a lifetime? Thousands, certainly. But tens of thousands? Millions? Probably not. Salman Khan is a teacher, too—with over 25 million students.

But how can one man teach so many people? With the help of the Internet, of course. Salman Khan is the founder of the Khan Academy, an online organization dedicated to providing anyone, anywhere, with a free, world-class education.

The project began when Khan, who has degrees from both MIT and Harvard, began teaching his cousin mathematics over the Internet. Many of Khan's other relatives wanted his help, too, so he decided to begin making educational videos and posting them online.

The academy's website features links to over 2,400 courses, covering subjects from math to the history of art. The lessons take the form of YouTube videos followed by several practice exercises.

One of the most important things about these videos is that they're available in languages other than English. At present, Khan's lessons are available in 65 languages. This means that anyone can use the service, no matter where he or she is from, what language he or she speaks, or how much money he or she has.

一般而言，教師畢生能教導的學生人數能有多少？肯定會有上千人，但不一定能達到上萬人或上百萬人的境界。薩爾曼•可汗也是一名教師，但他的學生卻超過2500萬人。

但單憑一己之力，怎麼有辦法將教學觸角延伸至這麼多人？當然是借助網路的力量。薩爾曼•可汗是「可汗學院」的創辦人，此線上教育機構的宗旨在於為全球各地的任何人，提供免費的世界級教育資訊。

擁有麻省理工學院與哈佛學位的可汗，透過網路擔任表親的數學家教之後，即產生實踐此計畫的念頭。因為可汗的其他親戚也希望得到他的教學幫助，因此他決定自製教學影片並上傳到網路。

可汗學院的網站列有超過2400種的課程教材，科目囊括數學至藝術史。教學格式以YouTube影片呈現，影片最後還會提供若干練習題。

此類教學影片最重要的特色之一，在於不是只有英文的語言選項。可汗學院的課程目前已有65種語言的版本，意即無論使用者的居住地、母語 或經濟狀況為何，都可以使用此教學服務。