I wish that resources such as Khan Academy existed when I was at school. I don't know about you, but many of my high school teachers barely understood the material they were teaching.
I say this so often. And it's not that my teachers were dumb, but in a class full of people they may not have time to help those who are struggling on a topic or need a prior topic review.
I've always thought an interesting experiment would be to tell students to go watch the Khan videos before the class lecture. That way the teacher can focus on helping everyone get the deeper understanding in person rather than going over the basics. This seems like it would work particularly well with math.