Administrators have sent a letter to New Bedford High School teacher Joanne Maura saying she faces disciplinary action, including possible termination, for failing to report the assault.
The 18-year-old threw the chair last month when Maura confiscated the student's cellphone. The chair didn't strike the teacher.
School administrators say they didn't find out about the attack until a week later, when a video shot by another student showed up on YouTube. A hearing is scheduled for next week.
Maura tells WCVB-TV that the attack was reported immediately to the school resource officer and a housemaster.
The student has been suspended and faces criminal charges.