Teacher physically attacked

My 10 yr. old son came home Friday and told his father & I that at the end of the day he was in music class. They had a fire drill. As they lined up and walked to their designated areas (by the bike racks) he sat on a bike. The teacher screamed his name and to "get off" as she ran towards him....he said she grabbed the back of his neck, hard!...then twisted the skin as she let go. Then she clutched his shoulder (again he said "hard"!), moving him towards the line. He said he jerked away and raised his right arm while shrugging trying to get her to release the grasp and she grabbed his right finger pulling his arm behind his back. He said she started screaming at the class to "shut-up and stop acting like stupid idiots". He said they were allowed to return to regular classroom after drill and he reported the incident to his regualr teacher.
He rides the bus home, takes 40 mins, as he is telling his father & I the story the principle called to say she received the report. She said it was unacceptable... But that the music teacher told her she grabbed my son's ear, only. And that she was frustrated because the kids were acting up during the drill. The principle added the music teacher says my son has been giving her a hard time in her class. Later Friday evening the music teacher left a message on my home phone that she would like to speak to either parent regarding my son’s behavior in her class.
My son has her class only on Fridays for 45 mins. They just received report cards last week and he made honor roll, and received an award for "outstanding behavior". She marked his music grade as A, and conduct in her class as E (excellent).
My son has a bruise on his neck, which we have photographed, and has been voicing fear of returning to school and seeing this teacher.
I am meeting with school principle this morning (Monday) would like advice on how to handle. Do I allow school (ISD) to take control, or should I take my son to police station and file a report?
I do not want this teacher near my child again. Period.

Thank you for your input.
Sandy

Tell the principal that you will accept nothing less than a written apology from the teacher and that the teacher undergo additional anger management training. Otherwise, you will have no choice but to file assault charges against her. PERIOD!

It matters NOT what grades the child made or didn't make or the level of frustration of the teacher.

And do NOT reply to the teacher's call. Also instruct the principal that the teacher is not to call the home again and that any further communications will be handled by the office.