one major reason for all the cases is the illegal use of smart phones and social media. "Access is a key factor,"

Georgia: Epidemic of Teachers Accused of Having Sex with Students

...John Seryak, a retired educator who is now with the organization SESAMEnet.org -- Stop Educator Sexual Abuse Misconduct and Exploitation, says schools and police do not release official statistics, but his group's research, nationwide, compiled a list of 459 teachers arrested in the U.S. for sexual misconduct with students in calendar year 2014, and 496 more arrested last year.

Seryak believes one major reason for all the cases is the illegal use of smart phones and social media.
"Access is a key factor," he said.  "With students with cell phones all the time, and teachers with cell phones, there's that ability to communicate.... [some teachers] will actually target students they know are vulnerable."
But Seryak pointed out that the "secret" communications are also the reason many cases are exposed -- parents discover the teachers' sexting on the children's smart phones and laptops.

http://www.11alive.com/news/crime/epidemic-of-teachers-accused-of-having-sex-with-students/183630286