The debate is polarized. Both sides are entrenched in their views. And schools are caught in the middle, having to implement evaluations using value-added measures whose practical value is unclear.

Value-added models are a specific type of growth model, a diverse group of statistical techniques to isolate a teacher's impact on his or her students' testing progress while controlling for other measurable factors, such as student and school characteristics, that are outside that teacher's control. Opponents, including many teachers, argue that value-added models are unreliable and invalid and have absolutely no business at all in teacher evaluations, especially high-stakes evaluations that guide employment and compensation decisions. Supporters, in stark contrast, assert that teacher evaluations are only meaningful if these measures are a heavily weighted component.