That's the verdict of a federal judge, who on Monday sentenced Peterson to six years behind bars for fleeing to Mexico with the boy when he was 13.
U.S. District Judge Laurie Smith Camp said Peterson's maturity level "seems to be on the level of a junior high school student," and the boy's attorney agreed.
"Twenty-year-olds are not attracted to 12-year-olds - that's just not normal," attorney Amy Peck said. "She viewed herself as younger than she really was and didn't see it as inappropriate."
Peterson told the judge that she took responsibility for what she did, and said she wanted to move on with her life and make it better.
"I am not a sexual predator. That's not who I am," Peterson said.
But the victim, now 14 and starting 8th grade at another school, "is a changed kid," his attorney said.
"He is much quieter now," Peck said. "He's been through a lot."
Peterson was the boy's sixth-grade math teacher at Lexington Middle School during the 2005-06 school year, then started having sex with him in November 2006, according to court documents.
The pair disappeared in October, soon after the district's superintendent confronted Peterson about allegations of an inappropriate relationship with the boy.
She was arrested a week later in Mexicali, Mexico, after the boy made a cell phone call to his mother.
Peterson's lawyer, James Martin Davis, acknowledged that Peterson probably won't ever be able to teach in schools again. She's not off the hook on state charges, either.
In four years, she could be released from federal prison. She's being credited nearly a year for time she's already served., and could get another year off for good behavior.
In the meantime, her attorney said, she's a gifted teacher and hopes to use those skills at a women's prison in Pekin, Ill.
"I think she's got plans to teach math in the prison while she's there," Davis said. "She's already thinking along those lines."
Meanwhile, the boy is living in Nebraska with his family, his attorney said, but she would not say where except that it's not Lexington. She said there's no relationship between the boy and his former teacher, and "I would fully doubt if there will be a relationship in the future."
When Peterson was arrested, the boy "felt that it was my entire fault and felt terribly bad that Kelsey was in jail," he said in a statement provided by Peck.
Peterson "often told me that there was something special about me," he said, and she slipped him love notes after class, gave him beer and let him drive her car.
The Associated Press previously named the boy as police were searching for him but stopped using his name after authorities charged Peterson with a sex crime.
He was an illegal immigrant in the United States when he left with Peterson. He's been granted humanitarian parole by the Department of Homeland Security, and his attorney hopes to win permanent legal status for him and his family.
Davis has publicly questioned the boy's birth certificate, saying he was likely at least 16, and that he was the aggressor.
Peck and the boy's family have bristled at the suggestion, and neither Peterson nor Davis repeated it Monday.
Davis secured a plea deal for Peterson that stipulated a sentence of between 70 months and 87 months. By pleading guilty, she avoided a similar charge that would have carried a mandatory 10-year minimum sentence.
Peterson and her relatives and friends cried as they waved to each other across the courtroom and said, "I love you" after the hearing Monday.
"The next time I see you we can hug each other," she told family members, including her mother and father.
Her attorney says she's just glad it's over, but another chapter is just starting.
Dawson County Attorney Elizabeth Waterman said Monday that her staff will work to get custody of Peterson so she can face the state charges, which include kidnapping, felony sexual assault and child abuse.
"We'll be ready to gear up on ours as soon as we can get custody back," Waterman said.