Sal could not get to his cousin's house every afternoon to do math with her, so he recorded the sessions. She said she preferred the recordings, because she could rewind them and because he wasn't sitting there watching her not get it. He put them on the internet. Then he spent about fifteen years building an exercise engine, a "mastery" model, and a teacher dashboard around them, and told everyone who would listen that the point was to move the lecture out of the classroom so the classroom could be used for something better.

And the essay's premise is: this man wants your child to watch a video.