My evidence is empirical, but the consensus among the teachers that I've spoken with, HS kids transferring from CA are normally two years behind their peers taught in TX schools.
Don't know what it is for other states--any and all input is appreciated.
It's sad: I received my education in CA public schools when they were excellent. Every student in my 6th grade class was reading at 11th grade level or higher. One novel we read in class was Dumas' The Count of Monte Cristo.
They would still be very comfortable there now, the 11th grade is reading at a 6th grade level.