NEW BERLIN, Wis. – New Berlin school district officials reported this week that a 28-year-old high school teacher has been fired for allegedly having an “inappropriate relationship” with a student, Fox 6 reported.

The teacher, who had been employed at New Berlin West High School, is under investigation by local police, the news report said.

MORE NEWS: From Classroom to Consulate Chef: Culinary Student Lands Dream Job at U.S. Embassy in Paris

As shocking as such allegations might have been a few years ago, they are becoming more common by the week and month, in Wisconsin and across the nation.

In 2014, for example, the California Commission on Teacher Credentialing opened 328 investigations regarding teachers allegedly sexually assaulting students. That more than doubled the number of investigations from five years earlier.

Some researchers say the spike in abuse is due largely to the rapid growth social media, which allows teachers and students to communicate easily without detection by parents, peers or school officials.

And for every case of teacher-student molestation that gets reported, the suspicion is that many more incidents go permanently undetected.

One reason is a problem that predates social media – the traditional tendency of some school administrators to cooperate with local teacher unions and allow abusers to quietly resign, rather than endure the public humiliation of a sex scandal involving staff.

Many times the abusers are allowed to seek employment in other schools, sometimes with a positive recommendation from their former districts.

“The teachers union in most cases is the first posse that runs to the defense of the predator,” Terri Miller, executive director of Stop Educator Sexual Abuse, Misconduct and Exploitation, told EAGnews in a special 2013 report. “Essentially, it’s administrators and teachers unions who are usually the people … aiding and abetting child molesters in our schools.”

MORE NEWS: Know These Before Moving From Cyprus To The UK

Wisconsin media has been full of reports of teachers sexually students in recent years:

Last year a former Abbotsford math teacher was convicted and sentenced to four years of probation for having sexual contact with two students.

Last year a former North Fond du Lac teacher was sentenced to four years in prison for the sexual assault of a special education student.

Last year a former Menomonee Falls High School teacher was arrested after admitting to having sex with a 16-year-old student at least 12 times in a classroom.

In 2014 a Green Bay elementary teacher was charged with having sexual contact with an 8-year-old student.

In 2014 a former Messmer High School teacher was sentenced to four years in prison for having sexual contact with two students.

In 2013 a Milwaukee charter school official was charged with 14 felonies following accusations that he molested at least three students.

Those are just a few high profile examples found in a quick Internet headline search. The list of investigations, arrests and/or convictions is probably much longer.

And nobody knows how many incidents go unreported, sometimes in circumstances when school officials know about abuse, or have good reason to be suspicious.

One such case occurred in Madison in 2006.

A teacher was allowed to quietly resign in an agreement between the Madison district and the teachers union, after a female student accused him of touching her exposed leg and tapping her on the buttocks with rolled up papers, according to Madison.com.

The agreement, signed by a representative from Madison Teachers Inc., stipulated that the district would not notify the Wisconsin Department of Public Instruction about the girl’s accusations against teacher Anthony Hirsch.

It also stipulated that the district would give a “neutral” reference to potential employers – including schools – if contacted regarding Hirsch.

Hirsch went on to secure employment at Waunakee Middle School. He resigned in 2008 following his arrest for possession of child pornography and having a sexual affair with a different student when he was still employed by the Madison district.

There are no media reports of him molesting any students in Waunakee. He was later sentenced to four years in prison.

Waunakee school officials told the media that they were never alerted to the original accusations against Hirsch, which led to his resignation.

State law requires school districts to notify DPI whenever an employee resigns and administrators have “a reasonable suspicion that the resignation relates to the person having engaged in immoral conduct,” according to Madison.com.

The state defines immoral conduct as behavior “contrary to commonly accepted moral or ethical standards and that endangers the health, safety, welfare or education of any pupil.”

Art Rainwater, the superintendent of the Madison district at the time, told the media that “The district agreed that it would not file a report with the Department of Public Instruction regarding Mr. Hirsch because the conduct at issue was not of the nature that required a report be made,” according to Madison.com.

Rainwater also said “we were relieved” when Hirsch resigned.