A teacher slapped my child in the back can I sue?

another little boy saw the whole thing he's the one who told me first then my 8 year old confirmed it and he said after she slapped him hard in the back she said "Now Go Tell Ya Mama That!!I then went to the principle and when I walked into the office there was another angry mother with her son who said the same teacher slapped him in the back because he was writing in cursive the day before she hit my son. The funny part is she's not even my son's teacher.She had bus duty. I took my child to the e.r. and the doctor said he had a small abrasion. I know it's not that bad but she will hit another kid tomorrow if she's not dealt with.