A former Copperas Cove High School teacher is set to be sentenced to a total of 20 years on probation after she pleaded guilty to having an improper sexual relationship with a student in a plea deal with prosecutors.

Judge Trent Farrell, in 52nd District Court in Gatesville, approved a plea agreement for Amy Joanne Mainville, 30, which would result in her being sentenced to serve one 10-year term each on charges of aggravated sexual assault of a child and improper relationship between a teacher and student, District Attorney Dustin Boyd said.

Boyd said the terms would run concurrently.

The sentencing will be finalized after a defense expert witness completes and turns over a psycho-sexual evaluation on Mainville as required by the court, Boyd said.

Mainville was arrested after the mother of a 15-year-old student discovered several messages she “found to be inappropriate” on her son’s Facebook account, an arrest affidavit said.

"Due to the content of the messages, it appeared as if there may have been a sexual relationship," the police investigator wrote in the affidavit.

Under questioning, Mainville initially said the relationship was limited to the exchange of Facebook messages, the affidavit said.

But after a few minutes, the affidavit said, she told the investigator, "I'm tired of this."

She admitted to having a sexual relationship with the boy, who's identified by a pseudonym, and said that he came to her house at night after her children were asleep and that the two had sex, the affidavit said.

Mainville was fired in August, CCISD Superintendent Dr. Joe Burns said in a brief statement at the time of the incident.

"We had a parent notify us about a possible inappropriate relationship between an employee and a student. CCISD conducted an investigation and based on those results, terminated the employment relationship on Aug. 20, (2015)" he said.

"CCISD notified the Texas Education Agency as required by law," he said.

The affidavit said Mainville was terminated because of the Facebook messages before the police investigation began.