A Fox News reports offers 12 chilling examples of how tenure rules and unions protect truly awful teachers from the termination and other punishment they so richly deserve.

Academic tenure was put in place in U.S. school systems in the first half of the 20th century to protect teachers from arbitrary punishment, but in the last several decades it has morphed into something else altogether.

Typically earned after four or five years, tenure protects teachers from being fired without just cause. But when combined with the ability of teachers unions to fight tooth and nail over any accusation leveled against a protected teacher, tenure can keep bad teachers in the classroom or at least on the payroll for decades after initial charges.

Below are a dozen cases in which tenure and union muscle protected bad teachers, often at the expense of students:

Matthew Lang was a band director at O’Fallon Township High School in Illinois in 2007 when administrators learned he was having a sexual relationship with a 17-year-old female student. But instead of being fired, Lang was able to resign, and the relationship was kept out of his file so he could seek another teaching job.

“… we are asking that all information concerning the request for his resignation not be placed in his file,” read a letter from the teacher’s union rep to the O’Fallon school board that was originally obtained by education news site EAGnews.

The district complied and even provided a letter of recommendation that called Lang “an outstanding instructor.” Lang landed a job with Alton High School near the Mississippi River and about 15 miles north of St. Louis, Mo.He worked at the school until 2010, when he was convicted of molesting another female student and sentenced to six years in prison, according to the St. Louis Post-Dispatch.

Jon White was sentenced to 48 years in prison in 2008 for abusing ten students at schools in the Illinois towns of Urbana and Normal. But those victims might have been spared their ordeals if White’s past had been revealed.

He had previously worked in McLean’s school district, where he was twice suspended for viewing pornography on a school computer and for making sexually suggestive comments to a fifth-grader. Instead of being fired, the union-protected teacher was allowed to resign – with a letter of recommendation that made no mention of the incidents.

The families of students at Urbana Elementary eventually filed a lawsuit claiming that the Normal school District had misled Urbana, according to the News-Gazette of Central Illinois.

Click HERE for the complete list.