Thirty-year-old Joseph Stephenson of Franklin Township must serve at least three years of the sentence imposed Friday before becoming eligible for parole. He also must register as a sex offender and serve at least 15 years of supervised release once he's freed.
The former Delsea Regional High School coach pleaded guilty last October to sexual assault and officials misconduct charges.
Gloucester County prosecutors say Stephenson - who also was an instructional aide at the school in Franklinville - had a relationship with the teen between August 2009 and January 2010. He was charged after school officials learned of text messages the two had shared.