In the US, teachers' unions are in general against any objective measure of student progress. The unions are powerful beyond what you'd expect (with a UK persp

In the US, teachers' unions are in general against any objective measure of student progress. The unions are powerful beyond what you'd expect (with a UK perspective) because, in many cases, the body on the other side of negotiations (school board) is comprised of teachers' friends (often ex-teachers and even former union leaders) or family members. If you're interested in this topic, you might enjoy the book 'Race to the bottom'.