To understand what tenure has degenerated into (from the necessary protections for teachers that Ravitch writes about), it would be hard to find a better example than this:

A sex-worker-turned-teacher was granted tenure at a Bronx elementary school -- even as she burned up the Internet with blogs about her notorious past, The Post has learned.

In one posting, Melissa Petro bragged that colleagues who Googled her learned more than they wanted to know about her former life -- but either protected her or ignored the issue.

Teachers are recommended for tenure -- which virtually guarantees a lifetime job -- by their principals and approved by local superintendents.

Petro told her online followers that a "female administrator" at her school knew about her sordid past -- and warned her that her career would be in jeopardy if she didn't use a pseudonym.

The 30-year-old art and writing teacher ignored the advice, and it turned out her instincts were right.

Either nobody looked or nobody cared.

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