This is really critical, and in some ways goes back to the whole “No Child Left Behind” program from years ago, that still remains today. It connects predictions of student success to real student scores and then rates their teachers on that basis. Those rates have been held private, up until this year. Why is this a problem you might wonder? Well if you come up on this rating scheme with a poor rating as a teacher, those ratings would/could follow you to some other location where you seek to be employment.
There has been study after study, that shows that rankings of teachers based on a single years worth of kids, a single year of data are just not stable. Daniel Coritz of Harvard School of Education