LAKEWOOD, Colo. -- A Lakewood High School substitute teacher pleaded guilty Friday to having an inappropriate relationship with a 17-year-old student at the school.

Jon William McCarthy, 32, pleaded guilty to three felony counts -- one count of sexual assault of a child in a pattern of conduct and two counts of stalking.

The sexual contact occurred between October 2006 and October 2007 while McCarthy was working as a security guard and a student teacher at the school. He later became a substitute teacher and track coach.

The teen, who has since moved out of state, told one of her friends about the sexual contact and in April 2008 a student teacher at the school overheard a group of students talking about what had happened. She reported it to her supervisor.

A month later, McCarthy was arrested at the school following a police investigation.

The stalking charges carry a mandatory prison sentence which will be followed by sex offender intensive supervision probation. The judge will determine the length of the prison sentence and the probation supervision period at the sentencing hearing on July 31.