Pontbriand was accused of having a relationship with a 15-year-old student, who told police he and Pontbriand had more than 200 sexual encounters between 2002 and 2004. She was 32 years old when the encounters began.
During the trial, her lawyer called the former student a liar and a manipulator, saying he withheld details from police and at the preliminary hearing about his sexual relationship with Pontbriand.
In his decision, which is more than 150 pages long, the judge said there was a profound inequality between Pontbriand and the victim.
Pontbriand is scheduled to be back in court on May 8.