Only in recent years has the school system had the test-score data necessary to gauge whether individual teachers were raising student achievement. One result was that tenure decisions, made when instructors have completed three years on the job, were pretty much rubber-stamped.

In 2009, fully 93% of the teachers up for tenure got it, including many who had been given unsatisfactory performance ratings.

What should be a reward for good work has been little more than an entitlement. And that's just fine with the United Federation of Teachers.

Probationary teachers glide right into permanent jobs - and, not incidentally, into permanent membership in the union. Which is why former President Randi Weingarten, claiming tests are unreliable, snuck into state law a ban on using data in tenure decisions. And why new President Michael Mulgrew is suing Klein.