[_m8fo]

I have done research and haven't found that "plenty of schools have random assignment for students yet teacher A's students vastly outperform teacher B's students".

I'm very well aware of studies showing that teachers make an impact. That much is obvious. What I'm not aware of is any significant group of schools that regularly use random assignment.

[Retric]

Here is one interesting example: http://www.nber.org/papers/w21407 However, this really comes down to researches not being idiots.

If you mean at the school level, that's a policy choice which is far from universal. However, their are a lot of schools and a meaningful number do random student assignment.