Jill Lamontagne says she was just trying to help a troubled student when she exchanged dozens of emails and scores of text messages with the 17-year-old boy. Those online communications – including 94 text messages exchanged over a two-week period – turned into evidence that prosecutors used against her in a criminal trial after the youth accused Lamontagne of sexually assaulting him. The 30-year-old Kennebunk High School teacher was acquitted last week by a jury that found her not guilty of all 14 sexual misconduct charges that had been brought against her. Lamontagne’s trial highlighted the hazards of online communication in teacher-student relationships and illustrated the challenges school administrators face in trying to set effective policies. As technology becomes ever more pervasive and sophisticated, teachers are increasingly facing the question of how, and whether, to use online tools to reach students or families. “You have to be super, super careful,” said John Suttie, principal of Old Orchard Beach High School and the local superintendent.