Teachers are usually very good at some parts of their job but not as good with other parts. Determining how "good" a teacher is in multiple areas with very different learners is no small task.
Before we begin tattooing teachers with performance ratings, it might make sense to ask the more fundamental question: "Why?" Judging teaching to establish some sort of staff pecking order seems to be a hollow activity. However, if we are collecting data to determine how we can get better at what we do, now I think we have a legitimate purpose. Yes, these data will cause us to puff our chests at times and grimace with concern at others. But schools are about young people acquiring needed skills for a successful life, not about ranking employees. Achievement data, therefore, should be used by teams of teachers to make wise choices in planning how to increase their students' success going forward.
How educators respond to student achievement data is going to make all the difference as American public education climbs up or down the comparative international ladder. All this APPR attention in ranking teachers only confuses the improvement process. Unless the student has only one teacher from kindergarten until graduation, it is the composite effort of many teachers in a student's school career that matters.
Even if a single numeral rating of teaching was possible, such a rating is fleeting. Teaching is not like learning to ride a bike. A teacher has to be prepared to make regular adaptations to meet the needs of the next cohort of students. Teaching is an endless pursuit of finding the "best" way for each student to learn because, after all, it is our students' success (not the teachers') that is essential.
Inevitably there will be those who will point an accusatory finger at the people who do not support the APPR process as being "afraid of the data". Nonsense! To borrow a line: The data will set us free. But not just any data and certainly not silly data about teacher ability based on anemic sources (that are neither statistically valid nor reliable). We need to abandon the development of the APPR system (which I fear is politically motivated and not necessarily meant to help public education) and look for ways that can help teachers better meet the needs of kids. We need to quit being deluded into thinking that our classrooms are staffed by nincompoops who need to be branded with their ineffectiveness. At least ninety-five percent of the thousands of teachers I have known want to do their very best for the children in their classrooms (and we do not need the APPR system to detect the others). Teachers will not be humiliated into excellence. We will be much better off when we drop the development of APPR and explore ways that will assist teachers at what they are naturally inclined to do - get better day-by-day at teaching kids.