Comment by Karunamon

The problem is that developers and teachers are not assembly line workers, and any performance measurement metric you come up with will be optimized for with poor results.

Grade teachers on their students' test scores? Okay, now you have teachers spending inordinate amounts of time on overfitting the curriculum to the local standardized testing requirements and less time actually ensuring their students are educated.

Grade developers on their lines of code or number of features shipped? Be prepared for needlessly verbose code and buggy garbage shipped out to meet the metric.

Throw these objective criterion out the window in favor of a more judgment-based approach? Be prepared for lawsuits when the mistake is eventually made.