>>>You can't compare a teacher that has a class of 15 native english speaking, upper middle class, 2 parent house holds kids to a teacher with a class of 32 english as a second langurage, poor, hungry, cold, kids that are children of drug addicts, drunks, refugees especially using test written in English.

Nor should you, but hopefully no one is seriously suggesting comparing those two groups directly. What you can do is compare teachers to their peers in similar schools, and see whose students improve more over a given year. If an average student in Teacher A's class goes from reading at level x to x+2 in the course of a year, that's better than going from x to x+1.