I can see myself using it to learn things that my (admittedly lousy) teachers weren't able to teach. But, is it really true that teachers are straight up assign

I can see myself using it to learn things that my (admittedly lousy) teachers weren't able to teach. But, is it really true that teachers are straight up assigning Khan Academy material as part of the course requirements? That's interesting to me and I had no idea that was going on.