Bruce Baker is one of my favorite bloggers. He is smart and irreverent. He is not awed by big names. He actually was a teacher before becoming a researcher. He has the technical skill to crack the statistical analyses that others generate to make spurious claims. Unlike many with the same skill set, he is willing to call a phony a phony. You might say he is our Premier C.D. (Since I have taken a personal pledge not to use vulgarisms on this blog, I will give you a clue to help you figure out what a C.D. is; it is a Cr-p Detector).
In this post, Bruce shows what nonsense The New Teacher Project report “The Irreplaceables” is.
TNTP, you may recall, was founded by either TFA or Michelle Rhee, depending on whom you heard from last. Its purpose was to stock urban districts with shiny new teachers (like TFA) to replace those burned-out veterans with low expectations. Although TNTP is an advocacy group that seeks and wins contracts from urban districts, and although it has a self-interest in certain policies, it nonetheless turns out studies and reports to support its self-interest (fire bad old teachers, hire and retain new teachers). It is not surprising that advocacy groups crank out self-serving “studies,” but it is surprising that the media so often takes them seriously, sort of like taking advice from tobacco companies about the wisdom of smoking.
In his analysis of the latest bit of TNTP puffery, Baker demonstrates how unstable value-added measures are. He reviews the ratings for thousands of NYC teachers and finds that there are very few who remain in the top 20% every single year. In fact, he discovers only 14 in math and 5 in ELA out of thousands of teachers! He writes, “Sure hope they don’t leave.”
Diane Ravitch's blog 
The Rheesearchers at TNTP may have overlooked this little item in their review of DCPS teacher retention. On p.15 of this expanding organization chart, one finds the Office of Teacher Retention. Under the name of the director, in the box for staff listing, it reads: “Staff to be hired in coming months.”
I think of two classes I taught, back-to-back, several years ago. The first class was large (by my district’s standards), had many struggling learners, and there were kids whose homelives were not ideal. The following year there were only 15 students who came from stable homes. They had a work ethic. That first group is still struggling as it moves through our school system. The second group is for their teachers that one special group you get in your career. I don’t think I should take all the blame for the first group nor all the credit for the second. Our teaching skills don’t change: it’s the students who do.