This article I read a few moments ago is sobering. We are all excited about great teachers, however, how does a teacher become classified as great? Once a teacher is considered great, can that teacher maintain that classification year over year? How much is due to random error? Apparently a whole lot of it is error and more of it is fleeting.
"The papers discussed above do not report how many teachers are actually top-rated for three, four, or five years. However, based on my colleague’s discussions with a couple of the authors, it seems that only about 5-7 percent of teachers are rated in the “top” category for three consecutive years. It would be even fewer over four or five years (to ballpark it, using a 50 percent year-to-stability rate [as in this paper], only 1-2 percent of teachers will be in the top quartile for five consecutive years). Making things worse, many who are consistently top-ranked will be misclassified as such, due to random error"
Shanker Blog » How Many Teachers Does It Take To Close An Achievement Gap?
I have had some great teachers, but I wonder if they are still great? Have you ever had a really bad waitress or a really bad flight attendant? Do you think they were always that way? Or maybe they started out happy and effective and their productivity and customer care degraded over time. I imagine that after 20 years of teaching, a teacher may lose his excitement for the job a bit. He may become jaded and really want to choose a different career.
I know it happens in my line of work. Programmers who began with intensity lose the interest for coding and end up moving on to management, analysis, testing, sales, or just leave IT altogether.