LEBANON, Ohio — A teenager convicted of selling up to $20,000 worth of high-grade marijuana a month to high school students in southwestern Ohio was sentenced Monday to serve six months to three years in a juvenile prison by a judge who called him ‘‘a pretty fine young person that went down a bad trail.’’

Tyler Pagenstecher of Mason was taken into custody immediately after the hearing to be turned over to Ohio’s Department of Youth Services. The agency ultimately will decide how long the 18-year-old will be in prison, depending on his behavior.