In New York City in 2007, 10 tenured teachers out of 55,000 were fired for poor performance.
Ryan Sager at The New York Post has the full story of how teachor seniority practices impede progress in New York City.
First, tenure awards are essentially automatic. Teachers spend three years on "probationary" status, a time they could theoretically be let go. But virtually all of them are awarded tenure at the three-year mark. Even under Mayor Bloomberg, who's committed to tenure reform, the percentage of teachers denied tenure has ranged from 0.9 percent to 6.5 percent a year -- and that's including teachers who merely had their probationary periods "extended."
It doesn't end there. You simply can't get rid of a tenured teacher in this city. Take 2007, when out of 55,000 tenured teachers 10 were fired for poor performance. That's 0.02 percent.
How are the 99.98 percent of tenured teachers who face no accountability paid? Well, it's done in lockstep based on (you guessed it) seniority -- that is, time served. They can even boost their compensation by obtaining various degrees, all of which the data prove are worthless when it comes to teaching.
When layoff time comes? Yes, those decisions are based on seniority, too. Meaning that, in order to keep the longest time-server around, the most promising young teacher may be let go.