Every superintendent, or state commissioner, must be able to say, with confidence, ‘Everyone who teaches here is good. Here’s how we know. We have a system.

school-based administrators “don’t always have the skill to differentiate great teaching from that which is merely good, or perhaps even mediocre.” Another problem is the lack of consensus on how we should define “good teaching.”

Only about six percent of teachers are ineffective, she continues. For the remaining 94 percent, the emphasis should shift from ratings to learning.