A former Lexington teacher has pleaded not guilty to state charges for having sex and fleeing to Mexico with a 13-year-old student.

Kelsey Peterson is already serving a six-year prison sentence after pleading guilty to federal charges.

The 26-year-old former teacher appeared in Dawson County Friday, and entered a not guilty plea to charges of first-degree sexual assault of a child, felony child abuse and contributing to the delinquency of a minor.

Authorities say Peterson was the boy's sixth-grade math teacher at Lexington Middle School during the 2005-06 school year, and then started having sex with him in November 2006.