The quality of the teacher does matter, but OP says it’s not the constraint for most children. This is basic theory of constraints: a chain is only as strong a

The quality of the teacher does matter, but OP says it’s not the constraint for most children. This is basic theory of constraints: a chain is only as strong as its weakest link. The quality of a students education is a function of many variables, and the teacher is just one of those variables. This is why rewarding a teacher based on their classes performance is unfair. By luck they may either get a class filled with exceptional and privileged students, or a class of children with abuse and attention problems. The only way to really get a good measure the quality of a teacher, would be to control the quality of the parents, and all the other variables too.