A former Wisconsin high school teacher has pleaded guilty to sexually assaulting a 17-year-old male student after police found sexually graphic messages on her phone that revealed six months of sex romps.

Samantha Fitzpatrick, 29, took a plea deal in court on Tuesday after being charged with assaulting the teenager when she was an English teacher at Ripon High School last year.

Her sex assault charge carries a potential six years in prison.

Fitzpatrick was arrested in December last year after police received a tip that she was having an 'inappropriate relationship' with one of her students before she abruptly resigned before the summer break.

Samantha Fitzpatrick, 29, took a plea deal in court on Tuesday after being charged with assaulting the teenager when she was an English teacher at Ripon High School last year

During the investigation, a teacher at the school told police she had heard from a different student that the victim had been telling people he'd had sex with Fitzpatrick at her home.

Fitzpatrick was arrested in December last year after police received a tip that she was having an 'inappropriate relationship' with one of her students

Another student also told police that the victim had also said he had 'done stuff' with Fitzpatrick at the Comfort Inn hotel in Ripon.

A teacher also said she noticed flirtatious behavior between the pair and that the victim was often in Fitzpatrick's classroom sitting next to her desk.

She would pay close attention to the student and tune out the remaining students in the class, according to the teacher.

When the concerned teacher approached Fitzpatrick about the rumors, she chuckled and said: 'I could see how they would say this.'

They both initially denied the sexual encounters when confronted by police.

The victim admitted that Fitzpatrick often gave him car rides, but denied the two had a sexual relationship.

He claimed he only 'joked' about the romp sessions to his friends.

Fitzpatrick's sex assault charge carries a potential six years in prison

Another student also told police that the victim had also said he had 'done stuff' with Fitzpatrick at the Comfort Inn hotel in Ripon

But police quickly discovered a slew of racy and 'sexually graphic' Facebook messages between the pair, which included details of role playing and sex acts they wanted to perform on each other.

A search of phone records uncovered 67 phone calls the victim made to Fitzpatrick.

The teacher had deleted the student's number but investigators were able to recover it.

Some messages included Fitzpatrick professing her 'love for the victim' and asking the student to send revealing photos.

The Facebook messages between them stemmed from November 2016 to May 2017 before she resigned when details of the trysts became public.

As part of a plea deal, the charges of child enticement, exposing a child to harmful materials and obstructing an officer were dropped.