[mikeash]

I've never once seen a math teacher who got more than half the class to really properly "understand" in the way that's described. I've had teachers who went by the book, I've had teachers who ignored the book. I've had teachers who were boring, I've had teachers who were incredibly engaging. None of them really reached most of their students.

[nudetayne]

My differential equations professor had a 98% passing rate for that class over a 20-year span. He was an ex-Bell Labs and later Lockheed employee though, so he actually knew the material and how to teach.