FRESNO, Calif. -- Math may be the most important subject for a former middle school teacher on trial for sexual activity with a student.
33-year-old Justine Nelson is facing two felony counts -- one for sex acts with a boy when he was 13 and one for sex acts when he was 14.
Nelson admits to committing sexual acts on an 8th grader, but she's admitting to no crime.
"You can't find someone guilty if they're mentally or physically coerced to do something," said her defense attorney Roger Nuttall.
He says Nelson finally gave up and sent nude photos and engaged in sexual activity with the boy after repeated threats to expose their close relationship.
RELATED: Former Fresno Unified teacher testifies, admits to sexual relationship with 13-year-old
"She wasn't the aggressor," Nuttall said. "He was the aggressor."
He highlighted testimony from a psychologist who said the former teacher isn't a sexual predator, so he told the jury the boy was the real predator.
From prosecutor Liz Owen's perspective, Nelson was supposed to be the grownup in the situation.
"Mr. Nuttall wants you to believe the 13- and 14-year-old eighth grader had all the power," she said. "Please. He was scared to death to tell what was happening."
The boy's age is a point of contention, and an important one because it could be the difference between eight years in prison or three.
He testified he was 13 when the sexual activity started and 14 when it happened for the last time.
RELATED: Ex-Fresno Unified teacher performed sex acts with 14-year-old boy: Prosecutors
But Nuttall called the boy a liar who changed his story -- from saying it happened three times, starting when he was 13, to saying it happened dozens of times, mostly when he was 13 -- all to make money in a civil lawsuit.
Owen says the boy has consistently said it happened when he was 13 and when he was 14.
And she says what Nuttall seems to call threats is just a persistent thread of sexual conversations and photos and talk about her giving him money or clothes, but making sure his mother and her husband didn't find out.
"They want you to believe she had to do this, she had to orally copulate him because he was threatening her," she said. "There's no evidence of a threat. He never said if you don't give me these shoes I'm going to reveal this."
Nelson's teacher's credential was suspended after her arrest in 2016 and the California Commission on Teacher Credentialing revoked it in January of this year.
The jury in her felony case started deliberations late Monday afternoon.
California teacher admits to sex with 8th grader but says she committed no crime