From Bellwether’s new report, “Teacher Evaluations in an Era of Rapid Change: From “Unsatisfactory” to “Needs Improvement”:

Nationwide, it’s rare to find examples of districts dismissing teachers for poor performance. A recent analysis of New York City schools found that the district fired a total of 12 teachers, out of 75,000 citywide, from 1997 to 2007.36 This means that only 0.016 percent of teachers were dismissed over this 10-year period, a very low percentage given the numerous challenges within the NYC school system. The entire state of New Jersey dismissed 23 teachers for poor performance between 2012 and 2014 (out of more than 100,000 classroom teachers statewide, this represents less than .02 percent)…

Failure to differentiate high- and low-performers also hurts students. According to research from the University of Washington’s Center for Education Data & Research, using seniority as the sole factor in making layoff decisions forces districts to pink-slip more teachers. Because less-experienced teachers earn lower salaries, a district has to lay off about 10 percent more teachers to achieve the same cost reductions as an across-the-board cut.43 Because a policy that relies on seniority and ignores performance will force districts to lay off both high- and low-performing employees, rather than only low-performing ones, the overall result is a less effective teaching workforce. It seems ludicrous to purposely dismiss a great teacher while retaining poor ones, but some school policies on tenure and layoffs do just that.