Local school districts have started to grade teachers based on student test scores, but the early results suggest the effort deserves an incomplete.
The new type of teacher evaluations make use of the standardized tests that have become an annual rite for American public-school students. The tests mainly have been used to measure the progress of students and schools, but with some statistical finesse they can be transformed into a lens for identifying which teachers are producing the best test results.
At least, that’s the hope among some education experts. But the performance numbers that have emerged from these studies rely on a flawed statistical approach.
One perplexing finding: A large proportion of teachers who rate highly one year fall to the bottom of the charts the next year. For example, in a group of elementary-school math teachers who ranked in the top 20% in five Florida counties early last decade, more than three in five didn’t stay in the top quintile the following year, according to a study published last year in the journal Education Finance and Policy.