There’s a fascinating and informative column at Slate today that explains how teacher tenure has evolved into the reform-killing obstruction that we know today. As Bryan Caplan explains, though tenure began as a way to protect teachers from being replaced for political reasons or at the whim of powerful families, it has become a guarantee of a job for life:

Until the early 20th century, teachers had few protections. According to anecdote, they were fired for flunking the children of powerful parents, holding unpopular views, or simply getting old. Politicians sometimes replaced teachers as part of the infamous spoils system. … [Today] most teachers are fired for misconduct rather than simple incompetence. The New York City School District, which employs more than 80,000 teachers terminated 25 tenured teachers during the 2008-09 school year. Just two of the firings were based solely on incompetence. Less than one-half of the districts surveyed in one study reported dismissing a teacher for poor performance in the previous five years.

Emphasis mine, because it’s pretty shocking, when you think about it. New York City’s schools aren’t exactly paragons of educational achievement, yet only two teachers in ’08-’09 were fired for not being good at their jobs. That is a crazy figure. And we have teacher tenure to blame for it.