Disagree. The tails of the distribution are where the teacher effect is probably the least, because there are significant obstacles on the low end that make focusing on learning impossible and immense innate talent at the high end where the kid would learn if you put him in a closet with the textbook and a flashlight. The real problem with teacher success metrics is that they are outcome-based. It is no more useful to measure the success of a world class surgeon by including the outcomes of people who completely ignore the post-op care directions and instructions for lifestyle changes.