A teacher one standard deviation above the mean effectiveness annually generates marginal gains of over $400,000 in present value of student future earnings with a class size of 20 and proportionately higher with larger class sizes. Alternatively, replacing the bottom 5-8 percent of teachers with average teachers could move the U.S. near the top of international math and science rankings with a present value of $100 trillion.
I am using this post to save the link because I haven't yet read the paper. But if this is true, which I wouldn't find surprising, then... Wow.
HT: Greg Mankiw