WOBURN — A former Hudson middle school teacher who is accused of raping a student several years ago is now banned from working or volunteering with children. Caitlin Harding, 37, of Wellesley, pleaded not guilty Friday in Middlesex Superior Court to several charges in connection with the rape allegations. Judge Hélène Kazanjian released Harding, who was arraigned via videoconference, without bail, but ordered her to have no unsupervised contact with children younger than 18 and to not work or volunteer with children. Authorities said Harding was a teacher at the Quinn Middle School in Hudson when she sexually assaulted the victim, a 13-year-old seventh-grade girl, multiple times over several months in 2010.