A former teacher from Bucks County has admitted having sex with a 17-year-old male student. 39-year-old Gabrielle Marvelli of Quakertown pleaded guilty to a misdemeanor charge of corrupting a minor Wednesday in Lehigh County Court. She had sex with the boy at the Econo Lodge Motel in South Allentown the weekend of the senior prom at William Allen High School, where she had taught business classes from 2007 until the incident occurred. The Lehigh County District Attorney says it took place a week before they boy’s 18th birthday, and Marvelli could not have been prosecuted if it happened after he turned 18. She is a 1990 Wissahickon High School graduate who taught in the Quakertown schools before getting the Allentown job.