Salman Khan’s free math and science videos have moved from YouTube to classrooms, reports the New York Times, which looks at a San Jose charter school that’s using Khan’s lessons — and student-tracking software to teach ninth-grade math to students at very different levels.

(Teacher Jesse Roe) can see that a girl sitting against the wall is zipping through geometry exercises; that a boy with long curls over his eyes is stuck on a lesson on long equations; and that another boy in the front row is getting a handle on probability.

Each student’s math journey shows up instantly on the laptop Mr. Roe carries as he wanders the room. He stops at each desk, cajoles, offers tips, reassures.

The Khan-enabled classroom makes it possible to target instruction to each student’s level, while mapping each student’s math comprehension for the teacher. While some see Khan’s mini-lectures as too “sage on the stage,” the net effect is to turn the teacher into a “guide on the side.”

Diane Tavenner, chief of the Summit chain of four charter schools, turned to Khan to teach the fundamentals after small-group problem-solving proved  slow and unreliable.

Khan Academy remains free, thanks to foundation support.