Over the past decade, the free instructional website Khan Academy has transformed how tens of millions of students across the globe perceive and approach math. Now, it’s pursuing a bigger aim: ...

In 2006, Sal Khan started making YouTube videos meant to help his nieces with their math homework. Since then, Khan’s video collection has grown into a huge repository of tutorials used in and out of ...

"This," says Matthew Carpenter, "is my favorite exercise." I peer over his shoulder at his laptop screen to see the math problem the fifth grader is pondering. It's an inverse trigonometric function: ...