Why do the five categories appear to be different sizes?
As before, each category contains roughly the same number of teachers — one-fifth of the total. The earlier graphic displayed teacher ratings using a percentile scale. Although familiar to most people, percentile rankings do not show how much more or less effective one teacher is than another. They tend to exaggerate the difference between teachers who are near average and minimize the difference between the least effective and most effective teachers. The new graphic is scaled to more precisely show the distance between each teacher’s rating and the average. Why are there so many more teachers in the database?(Back to top) In our initial database, we only published ratings for teachers who had at least 60 students with English and math scores in two consecutive years. We set that standard because it limited the database to teachers whose ratings came with a high degree of confidence. In the new database we show the actual degree of confidence for each rating, providing additional tra
